Your friends make fun of you because they are insecure about themselves. When one person starts it, the other ones do too because they don't want to be picked on. The best ways to solve this are to:
A: Walk away, but dont let them say something like this "yeah keep walking cuz you know you're scared of me!"
B: Ask them to stop
C: Find new friends
Never get in a fight with them cuz they wont leave you alone they'll just keep messing with you.