My DM, DSis and I planned a girly day for the three of us. Nothing extravagant, just lunch and shopping. We asked my DF if he wanted to come, we knew he wouldn't but we always ask to try and minimise him getting annoyed at us going out without him.
The morning comes for us to go and he is in the garage repairing his bike. I mention that me, DSis and DM are leaving now in a casual way but I'm bracing myself for his inevitable bad reaction as I know it's coming. He immediately starts up "Oh great. So I'll just have to stay here then". I remind him that he can come too and that we won't be long anyway. He then starts an argument saying we never do anything with him, we treat him like sh*t, etc. He expects us at this point to not go and previously we wouldn't have, but we just put on a nonchalant act and say "ok well you were invited, we are going now" and we go. On the way I get a text implying he will smash things up in the house and writes "you'll see when you get back". We know this is just his typical pattern of behaviour so we ignore it but it ruins our day anyway as we all just feel really down.
We get back and everything is fine and normal. He acts like nothing happened. Later that evening when I see him in the kitchen he accuses me of ignoring him and not speaking to him when I hadn't seen him since we got back anyway. He apologises for the argument and I stupidly accept it. That's how it always goes. But I know this isn't just an argument, it's awful treatment but I don't know how I can tell him that it's just not acceptable.