Simple, two methods I would take into consideration is Mystery's Method of Rejection or Adam Lyon's (AFCADAM) rejection theory. Both work in similar ways but Adam Lyons is more subjected to the UK's norms. Mystery's Method is to just brush them of and say "Haha *don't emphasise the laugh* ok nice meeting you" (if you build social proof at the end of the night then they'll look like idiots, not vice versa). Adam Lyons has a little more depth into it, if he gets rejected he would say "Ok, sorry for bugging you *sigh* nice meeting you" and the same method applies, if you build up social proof later they'll look like total idiots, not you.
Happy Gaming
M