My friend, which is also my coworker, likes to organise events for his friends. He invites a lot of people, but always expects everyone to join him regardless of if they have already planned something for that day.
Since I'm one of his co-workers, but we work in different locations, he uses Skype to ask me. This is our conversation that started yesterday. We're Germans so the texts are loosely translated. (Edited to hide personal information)
Him: hey, want to go to the movie? I'm gathering some friends.
Me: maybe, what movie and when? :)
Him: To the new ***. Next Friday at 8. We might go for some food afterwards.
Me: ah, sorry man. Got something planned for then already.
Him: can't you reschedule that?
Me: nope, had it planned months before
About 2 hours later
Him: where would you like to get food after the movie?
Me: nowhere, I won't be there
Him: let me know if you change your mind
A bit later
Him: What do you think of **** restaurant?
Me: no idea, never been there
Him: here's the menu (URL). Choose something in advance so we can order ahead Friday.
Me: won't be necessary. I won't be there.
Next day, in the morning
Him: Don't forget to send in your order for Friday.
At this point I started ignoring him
Him: you'll be there right. I can count on you?
Me: I already promised others. I can't come with you guys and that won't change
Him: we're with 9 already. One more and we can get a discount.
Me: Don't expect me to help with that
Him: think a bit about it. I'll message you again.
I think I have made clear enough that I can't come and told him I was busy that night. Yet, he still doesn't seem to accept that as an answer. This happens every time he plans something, and I'm getting really tired of it.
How can I make clear to this person that I can't come and that he has to accept that?