After the thumping I got on AIBU yesterday, I've decided to try posting here instead
basically ds1 (8, with AS) told me last night that there was a SEAL activity at school tomorrow and I was meant to go to it - first I had heard of it, I was a bit annoyed but I did want to go
so having cancelled my afternoon's plans, left work early etc I turned up to do it with him
he behaved atrociously 
shouting, making fart jokes and being rude at the top of his voice, getting his friends to laugh at me etc
I can handle him - and I do, at home - but it was really difficult being in school with the teacher and the TA and lots of other parents there
I did actually take his chair off him and make him stand up, after three warnings for rocking it back and laughing at me when I told him not to
I feel utterly humiliated, and upset, and angry
and I am embarrassed that I was gruff and upset when the teacher asked me if I had enjoyed myself (she's great, it's not her fault at all)
and yes I KNOW he has AS and strange situations trigger him, and I know my feelings are childish and not his problem - that is why I am venting here, while he is at afterschool club (he announced loudly that he didn't want to come home with me, he wanted me to go home and to go to afterschool club as normal on a thursday)