My students keep calling me "mommy" and making sexual jokes

I'm (30) currently doing the first internship of my pedagogy studies, and also work at a local high school teaching english and social studies. In one of my classes, several of my male students (16-18) have a tendency to call me "mommy" and asking intimate questions (I apparently share a name with an intimate piercing, which they love to ask if I have). I have no problem with an accidental "mom". I actually find those slip-ups sweet. These boys are doing it on purpose to be crass, though. I've tried to play it off and tell them they are being inappropriate, but I'm not sure how to deal with the behaviour. Anyone else have the same problem, or have any tips on how to deal with it?