A no-brainer, you would think. This boy swears at, makes racial slurs at, hits, shoves and generally abuses my son. Despite this, DS has tried to be his friend, in the way that 6yos do. No amount of 'stay away from him' and confidence-boosting activities etc, has really helped, unfortunately. I've been in close contact with the teacher but to be honest, she hasn't been very effective in stopping his behaviour.
So I just try to help DS day-to-day deal with the situations he comes up against with this boy. It's actually been improving the last month or so, DS has started to really hold his own a bit.
Anyway. DS has a birthday coming up and we've booked him a party. Invites went out a couple of weeks ago to the children on the list DS wrote, not including this boy for obvious reasons. This was difficult for DS, who wanted to invite him because 'he'll be really angry if I don't, he'll push me' 
DS says the boy realised he's not invited and has been very upset with him. Trying to snatch the invitations from other people, generally being not very nice about it. Expected.
But now his mother has messaged me on Facebook demanding to know why her son is being purposefully excluded. She's written all over the closed FB school group about 'someone' excluding her son and how upset he is. She's asked on our local community page if the venue we've chosen for DS' party allows members of the public in during certain times (the time of the party).
I'm fucking gobsmacked tbh. I've never encountered anyone like her in my life.