I would look the pro dead in the eyes while breaking the cue over my knee, not say anything and walk out.. lol for real if I liked how it played I would play with it, if not then I would keep it just so I have a good story.
edit: Oh and on a side note I did beat Jeanette once. It was one of those pay xx to play a pro at a APA nationals event. I think it was $20 to play her, one rack of 9 ball, you win and you get her glove. I racked my own rack, broke, got nice spread and ran out. So I didn't really 'beat' her but still got the glove. I looked at her and said "I'll be practice room 4 later tonight if you want to win it back." it was quickly followed by "I'm just joking, that was pure luck, please don't hurt me.".