Charles:
When he's nervous he uses very long and difficult words in his, usual simple, conversations. You nearly need a dictionary to understand him.

Erik:
When he is nervous he makes the small coin he always has float into the air. To get his attention back you usually take it out of the air and run away. He will smirk and ran after you.

Hank:
When he is nervous he will play with your fingers. It can be cute at times but when you are reading a book or something it can get very annoying.

Sean:
When he gets nervous he will make cheesy comments like, did it hurt when you fell from heaven? Do you have a map because I got lost in your eyes. You will most of the time just place your hand over his mouth to shut him up.

Alex:
When he gets nervous he bites his lip and let me tell you one thing. It's freaking attractive. It will most of the time result in a make out session.

Pietro:
When he's nervous he will tap his foot. Just imagine him tapping and tapping with his super speed. Once he made a hole in the floor just by tapping his foot about 100 times a minute.