How to get my boyfriend to react when a guy hurts me?

Ive been dating this guy named Colby off and on for about 2 years now. But we have made it official now. He has always understood me,stuck up for me, and realizes my emotions and what not lol...but today i went to the mall with him and his cousin (Devon,who i don't like and is a bad influence on Colby) just so happen to show up. He said some really hurtful things to me but Colby didn't do anything about it. (he didn't laugh by no means!) then one of Devon's friend came and was reading my shirt which said "Myrtle Beach" and said "Myrtle *****?are you a Myrtle *****?!?" and it hurt my feelings (that was all he said but still..) and I basically had to ask Colby to do something about it...how do i tell him that id like to not have to "ask" him to make guys stop when they hurt me like that?