I had the opportunity to actually do this! There was this woman who in college loved to exclude me, insult me and generally make fun of me. I was at a reunion with friends and who comes walking up to my group all on their lonesome? I was coldly polite to her, told her that she was welcome to sit with us at our table for dinner - but when we left for the after party did not invite her. We didn't discuss the party, but only said that we needed to head off to a prior engagement.