So angry I could scream..Oh wait! I already did!!!

I got a call tonight from a mom of a child who is a friend of Robbie's stating that Robbie was picking on her son at school. Mind you this is the second time I have gotten a call from her in the last year about stuff my son is supposedly doing to her son. She informs me that Robbie pulled her son's hair on the school bus, talked smack to him on the football field and was talking about her son behind his back. Now I am the first one to say my kid is not perfect and completely believe he probably did do some of this stuff but then I wonder what her kid has done. So Robbie gets home from his football game and I tell him what she says and he doesn't deny any of it, so I start to get angry even more b/c some of me wanted him to be able to deny it and say he didn't do it so I could call her back and tell her to shove it. But I can't, plus that is just immature and the anger talking. I got to have over an hour conversation with him about how sometimes words hurt peoples feelings and obviously this child can't deal with it and he needs to just stay away from him completely at school. Part of me wants to say "Boys will be Boys" and just write this off but I have worked way to freakin hard in my life to give my children what they need and to provide for them and be a good wife and mother. Robbie is devastated that he is getting in trouble b/c he is not the only kid doing this stuff but this kid doesn't tell his mom this and makes it like Robbie is this bully and something is wrong with him. I just don't know what the right punishment is for him b/c while some of this is just crazy to get upset over b/c kids joke around all the time but we do not raise him to be mean and that just because other kids do it doesn't mean he has the right to do it. He plays football and takes guitar lessons and I was willing to take them away for a week but hubby is not b/c he thinks I am overreacting. My next option was to make him clean the bathrooms for a week but am not sure if it what I should do. Oh I just want to scream, maybe you could help me out?