My friend gave me a few great ideas so I decided to type them out.

Marinette:

She felt a bit jealous when she saw how good you are at making clothes. She considered this hobby one of the things she's best at, so seeing someone else better makes her feel jealous. She knows it's not good to get jealous at her lover's success, but she can't help it.

Ladybug:

When she saw how good you were at coming up with plans, she was amazed, praising you for your intelligence. When you chuckled and said you were always this good at coming up with plans, she gave you a smile and said that's a good talent to have.

Adrien:

He never considered himself very good at the piano, so when he heard you playing it so beautifully, he was in awe. He sat aside you, trying to be as silent as possible not to disturb while he watched your fingers, amazed you can do all these moves with your fingers. When you finished, he gave you a smile, saying that was very good before he curiously asked you what the most complex song is that you can play, asking if you can help him with his piano lessons, hoping you say yes so he can also spend some more time with you and his boring piano lessons become a bit more fun.

Chat Noir:

When he found out you are better at jokes, puns and flirting than him, he immediately had to put that to the test. Both spend hours saying jokes, making puns and flirting until someone laughed loudly at the jokes/puns or looked as red as a tomato from all the blushing at the flirting.

Alya:

When she saw how good you are at filming things, she got excited, saying you can film the videos and she will edit them and upload them to her blog, so teamwork. She loves it a lot whenever you send her a video of the heroes you filmed for her, happily thanking you and getting the video ready to upload onto her blog, giving you the credit you deserve for your good filming.

Nino:

When he learned you are better than him at being a DJ, he was quick to tell you to teach him, saying he really wishes to improve so please help him. He enjoys the moments where you teach him a lot, he finds them very fun.

Chloe:

When she learned you are better than her at something, she let out a gasp, saying nobody can be better than her at something before she stormed off to go confront you and ask what you are planning, or to either go and practice some more so she can get better at it and show off how good she is.

Nathaniel:

He felt annoyed whenever you showed your art. He wanted to say that he knows you are better and his art is bad so no need to keep showing it, but he kept it silent and gave you a little smile, mumling that's good, because he knows it's just his jealousy so he shouldn't act on it and if he keeps practicing he will also get so good at drawing.

Luka:

He was amazed at how good you are at the guitar. When you finished the song, he clapped his hands, praising you before he asked you where you learned this and how long it took you to get so good. Both had a long talk about music and playing the guitar.

Juleka:

She didn't mind that you were better at makeup than her, she liked whenever you taught her some tricks. When you taught her how to make a realistic-looking cut, she was amazed, saying your talent is amazing and she hopes she can get this good one day.

Marc:

He didn't like it. He was happy for you, but it made him feel useless and as if his writing is bad. He even thought of giving it up, mumbling that you can do it better anyway so no need for him to keep going, but luckily you managed to convince him to keep going.

Gabriel:

He refused to believe that, even going as far to demand you both have a catwalk with the clothes you both designed to see who has better clothes and who people pick. But after some thinking, he realized this could be good business for you so he offered you both design some clothes together, claiming it can bring in some good money.

Rose:

When she saw how good you were at scrapbooking, her eyes widen with amazement before she excitedly told you to teach her how to do that so beautifully because hers always look like a mess. When you chuckled and said she's sticking too much in it, she blushed and said she doesn't have enough scrapbooks so she just keeps adding in the already-full ones.

Alix:

When she saw how good you are at rollerskating, she was amazed. When you took a break, she skated over in a hurry before excitedly saying that was so badass and you have to teach her how to be so good and look so cool while doing it.