Alec: you bite/nip on his neck when he needs to be working

Jace: refuse to get up. From bed or the table wherever you are

Magnus: hide his magic stuff from him. You only do it because you want to spend more time with him

Raphael: disappear for hours without telling him. You don't do it on purpose but it is funny to see him freak out.

Simon:mock him. Especially when he's trying to be serious

Sebastian: poke his face repeatedly. Like when he's taking just "boop" his face.