Tony
Biting your lip and chewing on your cheek. You always did while you were thinking or working on something. He loved it because it was cute and you never noticed him while you did it, leaving him to watch you longer than you usually would let him. Whenever you did catch him staring he would sometimes ask, "My turn?" Insisting on biting your lip himself.

Steve
Talking to yourself. He thought it was so funny when he came home from work one day and you were just muttering to yourself. You only do it when you feel lonely so he tries to be quiet coming home just to gear your personal conversations to yourself.

Bruce
Quoting anything. You didn't just quote the quote, you did a huge chunk of dialogue and would play the parts and voices.

"But what about Brad? I mean, he's like a brother to me!"

"Your a good man."

"I know I know."

Pietro
Walking on your tippy toes. You did it ALL THE TIME. It wasn't good for your ankles but Pietro LOVED it, he thought it was adorable and that you looked like a cute dancer strutting across the stage. Whenever he caught you doing it he would say, "Dance for me?"

Bucky
Drawing. You drew on everything, napkins, windows, walls, you, you even doodled on Bucky's arm oncr. And when you didn't have a pen or pencil you would make imaginary lines with your finger and trace patterns with it. He loved your creativity and how peaceful you looked doing it.

Thor
You loved taking pictures. Of everything, mostly him though. He thought you booked so cute with your little camera running around snapping shots.

Clint
Obviously pranking. You guys always had prank battles.

Loki

Humming. He thinks you have a really beautiful voice, he really loves listening to it.