It means he is trying to fit in.
There are a few clarifications I would need about your question to know how to answer it, however there are two answers I have at the moment. [1] If you mean that your boyfriend is nice when its just you two but is mean when he is around friends, then that is a BIG problem. You want to date someone who isn't two-faced like that. Don't let him push you around and be two different people. [2] If you mean that your boyfriend is nice, but his friends are mean, then you should talk to your boyfriend about it. You don't deserve that, and he should be sticking up for you. Also, what do you mean by nasty? Like perverted or mean?
get over him
Your friend is just trying to make you jealous just ignore them.
Hes using you. Maybe to show of to his friends or maybe jst to have a gf.
Heck nooooo!! Who cares what your friends think. My friends didnt like my boyfriend either but i didnt care. If they are really your friends and care about you they will let you be with whoever makes you happy. Unless hes mean to you but just talk to your boyfriend if he is really being mean to them.
It means they are stalkers
That he's embarrassed by them. Or that he doesn't think they'll act good around you. Or that he doesn't want to have to share you with them.
It means that the boy likes you or he is goin to ask you out
Unfortunately you have to simply tell him you have a boyfriend and are not interested in him that way.
it means that hes trying his best but he wants to just be friends
They mean that they do not want the relationship to extend to anything more than friends. They do not want to get into girlfriend and boyfriend.
It means he doesn't respect you enough act appropriatly. Dump him and find one with some manners.