I echo what others have said about something not quite ringing true.
You have your only son's side of the story, interpreted through his 16 yr old self-absorbed focus (and most teenagers of that age self-absorbed, no way around that).
It would be professionally suicidal for a teacher to behave in the way your son described, utterly unprovoked. There must be more to it than he is telling or noticed (see above).
If only more parents realised how very differently their children behaved whilst at school, schools and parents really could be singing from the same hymn sheet and doing a far more effective job. It's not wonder teachers feel stressed, being shat on (ha- can do it here!) by pupils, parents, management, the government, Ofsted, the media etc...
If more parents cut teachers some slack, and recognised that most nowadays are a)well-trained, b) models of restraint, c) in teaching because they believe they can make a difference, we could all stop worrying where the next specious lawsuit or complaint is coming from. I really do think that schools worked better when parents believed them over their own child...