It's a nasty assault, I wouldn't say serious and I'm suprised a chipped tooth and some broken cartalige warranted a charge for GBH Sec.20 (GBH without intent).
I would have said it was more along the lines of a serious Sec.47 Assault (ABH), just for the fact that 1. it's a chipped tooth, 2. cartalige is not bone 3. the defendant experienced verbal abuse and was "egged on" if you will. In other words if the "victim" had not persisted with his behaviour and conduct of harrassment, he wouldn't have been assaulted.
Saying that though, you can't just go around punching people in the face just because they say things you don't like.
If your friend has a good lawyer, he should be looking at a suspended sentance and paying compensation. I'm amazed the matter has gone to Crown Court though, what a waste of public money.