How to respond when you haven't been invited and other friends assume you have

[Rach168]

Just that really e.g. If the friends you are with all start chatting about going out to celebrate a mutual friends' birthday or other event and ask you whether you're coming (in a way that clearly assumes you know about it and were invited) - Do you tell them that it's the first you've heard about it/you aren't invited or do you just say 'no, I'm not coming'?

I used to be tactful and say I am not coming, but this gives a get out excuse to the inviter if they ask where you are. Now I just say I wasn't invited and leave it at that.