You’re son probably isn’t a bully, but it doesn’t sound like the other kid is ok with receiving these jokes either. I guess my initial thought was if this other kid was fine with the horseplay, why isn’t he dishing it out himself, and why would talk to his dad about it? I mean, @ junior high, you are smart enough to figure out what is considered PC and what isn’t. So if this was really just horsing around, the last thing I would want is to share it with my parents. It would be like hearing a funny, yet crude sex joke in middle school, and then going home and sharing it with your parents. Ewe…
That said, it would probably be in your son’s best interest to lay off the “little bitch” and the “yo mama” jokes at school. Eventually, it’s bound to be overheard his female peers, and then he’ll be in deep shit with the school’s administrators.