Steve:

Social Media - Obviously Steve grew up without the internet, so he doesn't understand it. He is particularly confused with social media and your love for Instagram, also he doesn't even know what Snapchat is.

Bucky:

Selfies - You enjoy taking selfies, particularly with Bucky. He doesn't understand them, particularly by how you're able to get such good angles and how switch the camera even though you've shown him a million times.

Pietro:

Swimming for Exercise - Pietro loves to run and he doesn't understand how anyone could prefer a different form of exercise. You on the other hand find swimming to be the best form of exercise for you.

Loki:

Dropping Sexy Hints - No matter how many times you do it, Loki still seems to never understand when you drop hints that you want him. You pretty much always ended up having to spell it out for him, but eventually gets it.

Clint:

Cosmetics - From face masks, to make up, to hair products, all of it confuses Clint which is why he constantly makes fun of you for them. You always get back at him for it though, but that doesn't stop him.

Thor:

Yoga - Thor saw you doing it once and didn't understand, so you tried explaining what it was and the benefits. He was still confused so you took him to class once, he did not do well, you laughed your butt off and decided it was the best idea you had ever had.

Tony:

Sing Along to Disney movies - Whenever you watch a Disney movie you end up singing along to all the songs. Tony doesn't understand the point, which is amusing to you because the point is basically to bug him.

Natasha:

Binge Watch TV Series - She can do movie marathons with you, but only if you guys take occasional breaks. She never understands how you can stay still for hours to watch almost an entire series in one sitting. 

Wanda:

Surprise Her - Since she's telepathic Wanda isn't used to being surprised. You though, have figured out a few ways to hide when you're thinking about doing something special for her so she isn't suspicious and doesn't read your mind to figure out what you're doing.