It really is the most amazing thing just do a little tinkly laugh, sat what you want to say and somehow come across not rude!
"Trebus would you like to come to this party?"
"No and you've only invited me last minute because you feel guilty tinkly laugh"
They laughed back and I did more tinkly laugh then backed away slowly. I can now see them on the other side of the room looking perplexed. Thank you tinkly laugh for giving me the courage to say what I think and get away with it without seeming rude!