Thanks everyone. I've always assumed a PDA aspect to his autism, but it is the degree of retribution he exacts that seems unusual - the taunting goes on indefinitely, long after (weeks after) the person has tried to rectify.
Yes - this is exactly how my DS can be.
We call it 'focusing in' - he becomes fixated on getting 'payback' for some kind of wrong he feels has happened to him, and he can then 'focus in' on that person for weeks.
It's very challenging and tiring to try and manage.
Keeping him in a calm, just right state helps because he's less likely to become angry / upset over things which in turn means he's less like to seek 'payback' (that's what he calls him) from someone.
But keeping him in that magical just right state is very very tricky.
When he's calm he's a kind, delightful boy - but it's such a delicate seesaw keeping him like that.
Really I have to be his 'buffer' most of the time he's with me - school remains difficult even with full time 1:1 and an EHCP.
TBH there are definitely personality types that work well with DS (laid back, funny and easy going types) and then there are ones that he constantly butts up against.
School (and I suppose later, work) forces you to socialise with people that you aren't naturally aligned with.
My hope is as he gets older he'll start to gather his 'tribe' of people who get and understand him.
But equally he will also encounter those who don't and I do hope we can help him develop coping strategies to deal with that (rather than the maladaptive 'you've annoyed me so I'm going to hurt and annoy you' ones he uses now).