Night out planned. Some people have invited themselves. Perfectly fine. We generally love them. Now they've invited someone else we've never met. Could be awkward/could be really good. Have very close family to this person and it ended in a huge fallout and me having a very big argument with them. I never argue, I am placid as a potato.
Either way, the whole attitude to the night has now changed because if this and now instead of being a fun night out its a family affair and everyone's on best behaviour.
You don't invade someone's night out and then bring more people along do you?
I'm being deliberately vague to remain anonymous. Sorry 