Scorpio that sucks, but if you have juiced to get where you are physically then even though he is an ass for saying it there's really nothing you can do.
If you haven't juiced to get to your size, next time he says it go haa haa haa(fakely) and then grab him two hands by the shirt and tell him, "I have worked really fucking hard to get where I am physically and if I hear that comment from you one more time you might regret it."
This way your assualting him and your getting you point across while probably making him piss his pants. He will think twice before saying it again.