I've read several posts by men saying that the obvious comeback to being teased in a locker room would be for your son to ask, "Dude, why are you checking out my penis?" Many men have said that any guy who starts commenting on another's foreskin status is likely to be the one who's made fun of, because making it obvious that you're looking at other guys' penises is just not done.
I'm always a little confused by the "everyone else is doing it" argument for circ. Fifteen years from now, if your son's peers decide it's cool to, I don't know, use woodburning tools to make designs on their scalps
, will your relatives be pressuring you to go out and get him a woodburning tool and some aloe vera for afterwards? If his high school friends start keeping scorecards of who's gotten which girls to perform which sexual acts, will Grandma be calling you all concerned about the lack of fellatio he's gotten?
Why on earth do people want you to do something to your baby based on peer pressure when later in life, they'll want that same baby to resist peer pressure?
My suggestion to you would be to refuse to discuss it. If you were feeling really secure and confident, I'd say, sure, go ahead and try to educate people. The problem is, a lot of people will take your willingness to tell them about your reasoning as an invitation to debate it with you. You don't need to convince them you're right. It's okay to say, "I'm not discussing this anymore. We've made our decision," and just repeat that every time they start saying, "But what if/Have you thought/I heard about a guy who..." If they don't agree, fine. You don't need their permission or approval. You're the Mama.