One kid told him he had a "small weiner" in the bathroom one day. He just ignored him so hopefully that will continue. But I don't doubt that there will be some teasing as he and my other son get older.
In a high circ area, I would most definitely arm my son (even when very young) with appropriate responses to any teasing. I would probably teach my 5 year old exactly what circumcision was (as in: When some babies are born, they have some of the skin of their penis cut off. I made sure no one cut anything off your penis).
Then I'd let him know that if anyone asks why his penis is different, or teases him about it, he can just tell them the truth in a simple, direct way: Your penis looked like mine when you were born, but the doctor cut off part of the skin on your penis.
If you are already getting teasing at age 5, I would definitely arm my son like this, so that he can protect himself and that he knows that HE is the lucky one.
I would probably do a lot of talking at home about how sad we feel for the little boys who had part of their penis cut off when they were too little to protect themselves.
Heck - I live in the UK, where no one is cut, and that is how my kids and I talk about it when we do talk about it (which isn't that often, but will probably become more often as they get older).