Well the language and behaviour of some kids is pretty disgusting and its very hard keeping our own kids away from it, just walking them to school can teach them some choice behaviours so its no wonder kids pick it up. I do think though that its up to the parents to speak to there kids about what they hear and let them know that its unacceptable and discuss with them why and what the consequence for copying the behaviour would be...and be prepared to follow it up if necassary. As someone has said in a post below use them as an example of how you expect your child NOT to behave as theres little you can do to control other peoples behaviour and its impossible to completely avoid. Also talk to him about how this girl must have felt when he pushed her and spoke to her like that...try to get him to empathise with her, perhaps some role play so he can understand that it was hurtful and if it were me I'd also have him apologise to the girl and her parents to show some responsibility for what he did to her.
Blaming teachers is no good, its the parents who need to teach their kids the standards they expect and everyones will be different (some find swearing and aggression acceptable) so it would be impossible for a teacher to find a set of standards that would suit every family.
