Sherlock;
He was uncomfortable, yet intrigued, about how he'd been feeling. And since you were desperately looking for anyone to go out with before your sister returned a total of four months early, he figured it would be the absolute best time to do so.
Entering the dimmed lab, his fingers fighting the material of his pocket, as he fidgeted out of control. His thoughts routinely circled between 'Oh god, he couldn't do this' and 'this was a terrible idea'. He always meant to take your pulse or see if your pupils dilated when looking at him, but he'd never gotten the chance. He couldn't look into your eyes without risking staring, and his own heartbeat rang too loudly in his ears for him to even register anything else whenever he got close to taking your pulse. He was going into this completely blind.
"Y/n..?" The place seemed darker than usual, but he eventually found you examining a corpse with a black light. The violet rays danced across the body, and there were little strings of lights reflecting back to the light, sparkling into your eyes.
"Hey, Sherlock! Come look- He's got 'invisible ink tattoos'!"  You chirped excitedly. Curious, Sherlock stepped up to you and the body, smiling at the intrigued glint your eyes held. The inked-man no longer interested him, his only thoughts were on the swimming emotions in deep E/c eyes.
"Interesting..." He murmured, not really looking at the corpse on the autopsy table. You had a few stray hairs dangling from the, once pristine, messy bun. You felt his long fingers before you saw them, and the blush immediately set into your cheeks. Masterfully, he tucked the little hairs back behind your ear, studying you like you were some kind of masterpiece.
"Um, Sherlock?" He was snapped from his thoughts, as going a bit wide when he realized the black light was now focused on him, and you swore he was blushing.
"T-They were hindering my view..." It wasn't until after he said it did he realize how it sounded.
"Of the corpse, of course. I-I wasn't st-looking at you, or anything..." A soft smile crept up your cheeks, knowing you hadn't been seeing things.
"Sherlock," you paused to let him finish his flustered babbling, "there's that forensics emporium opening in a few days, want to go check it out with me?" And that's how you asked the Sherlock Holmes on your first date. It's also how he ended up with a scalpel in his hand when he fell out of pure surprise.

John;
You could only hope John would ask you out. You never were very good at that sort of thing, always got too nervous to even speak. Hopefully he'd gotten the message you were interested in him, and (even more so) fancied you, as well.
You had to take your charts with you on your break, having more than just the usual patients. John brought both you and his coffees to the table, and he tried to occupy his mind, so he didn't stare.
"D'you need some help?" He offered kindly, and your eyes snapped up to look at him. You flashed him a grateful smile, and he knew that smile would be the death of him.
"That'd be absolutely wonderful. Thanks, I owe you one." You accepted, and he reached over, taking half the pile. Papers shifted as you enjoyed the other's general presence and alright coffee was sipped in generous douses. He glanced up at you as often as possible, before going back to filling out the general patient paperwork. Everything was done in pencil, except the final page, which had to be done in pen. Luckily, it was so little that you could share one between both of you. About four fifths of the way through what seemed to be the endless, tedious work, you reached over to grab it once more, finding a warm hand caressing your fingers. Your eyes shot up to find John's blues meeting your E/cs. He smiled softly at your delicate rose blush, as he laced his hand fully around yours.
"Would do you say you let me treat you to dinner tomorrow evening? You know, as a thank you for helping?" He offered, only a tad awkwardly. No way you were going to object to that offer.
"That would be lovely, John." The moment lasted a minute longer, before he felt the metal pen being pressed into his palm, alerting him that there was still a lot to get done.

Mycroft;
There never would be a 'perfect' moment for you to ask Mycroft to go on a date with you, but eventually, you decided to just go for it. This meant, of course, days spent planning the perfect thing to say, until you decided that you'd get too tongue tied, and that texting was a better option. That led to many failed attempts and unsent messages. Oh, poor you, though, because you forgot Mycroft could read anything you typed, with just a tap of a button. Lucky you, as well, because despite knowing you were trying to ask him out, he was having the exact same problem. Only he preferred not to text...
The eighth time he called you that week, and he finally thought he had it. You were just at home, typing up some reports when your phone rang. His umbrella was being spun in an attempt to calm his nerves, and your hair was twisting around your finger in the same fashion. It was time to act casual...
"Hey, Myc. What's up?" Okay, that was a total flop. Other than your voice going all over the place like a wonky square dancer, you rarely used such unpleasant word choice. Mycroft didn't seem to notice, and you thanked Chuck for that.
"N-Nothing much, really..." If the butterflies in your stomach would shut up for a minute, you maybe heard the tremble quaking in his voice. Attempting to gather himself, once more, determined to make this his last phone call about this one subject matter, he cleared his throat.
"Actually, there was something I've been meaning to ask you..." Too distracted by not getting your hopes up, and trying to finish this stupid report because your intern was an incompetent fool, you barely registered what he'd said.
"Yeah?" The response was passive, and suddenly he forgot everything he'd meant to ask you. He thought about hanging up... No, he was sick of this.
"I have a reservation for the symphony this weekend, and I figured I would use this opportunity to ask you on a..." He choked, and mentally cursed himself for doing so. You were now hyper-attentive to everything he said, and you could tell your heart would leave bruises on your ribcage.
"On a date?" You froze at the sudden question, and had to bite your lip to contain the squeals threatening to spill. Your excitement would definitely be audible, you realized, and you moved the receiver away from you. Collecting yourself, and pulling it back, Mycroft obviously wasn't at his cameras...
"You don't have to, of cou-"
"Nothing would make me happier." He swore he died in that moment.
"Delightful." You could hear the relieved smile in his voice, but you really couldn't blame him. Not with the cheesy grin spread across your face.

Moriarty;
Everything had to be perfect. Your favorite black Westwood, with the cool Armani skull tie, and crisp white double-collared button-up dress shirt. Knowing he was, at what you claimed, his best, he should've felt even the slightest bit less nervous, but it had yet to help any. He remembered when you mentioned your favorite flower, and he picked up three extra, just in case. All he had to do was ask... Simple, really. Just get it over with, like pulling off a band-aid. Only a thousand times worse, because his nerves were on such a high alert, he hadn't been able to eat because he was so afraid of puking.
"Lovely as always, darling. I was actually hoping that you wouldn't mind accompanying me to dinner sometime?" He rehearsed, being only four turns from your street.
"No." He mentally cursed himself for being so blazingly pathetic. Had it been any other human being on earth, straight men or homosexual women included, he could have them at his feet in a second- flat. But he couldn't do this, not when his heart sped at the mere thought of you.
"Goddamnit, Jim. Get it together!" He took a deep breath, finally turning onto your street, and pulling up at the curb in front of the cozy little home. Picking up the nicest of the four flowers, he smoothed out his hair in the rear-view mirror. He sucked in one more breath, before building up enough gall to actually go up to your door. One look through your peephole, and you could already see all the signs. Oh, no way were you prepared for this. Not in your towel, just getting done with your shower.
"One minute, Jim!" You sprinted upstairs, quickly pulling on one of your nicer dresses, drying your hair with your towel, then starting on your mascara. Soon, your hair was mostly dry, looking like it was put in purposeful waves (thank chuck, the one time it chooses to behave!) and you pulled a nude shimmer gloss onto your lips. You looked pretty good, you could only hope Jim would agree. As you rushed back down the stairs, pulling on a pair of suede black heels, and you were ready to go by the time you got to your door. Reservations at Lucci and Masons, check, date asking you out, check, and looking presentable, double check. Swinging your door open, absolutely adoring his stunned look. You plucked the flower out of his hand, his jaw remaining slack for a few more moments. You breathed in the gorgeous scent, before using it you hold back your hair.
"What? Not going to escort me to the car?" You teased, the smile broke out on his face, and he looked down, chuckling for a moment at, what could be considered both of your, usual antics. He offered you an arm, bowing slightly at the waist like a proper gentlemen.
"Should've known you'd manage something like this. Where to, darling?" He joked back, as you took hold of his arm. You giggled a bit, closing and locking your door behind you.
"Lucci and Masons, obviously. And yes, you should've."