Fun Bar Bet Game
You: I will make you a bet. All you have to do is not say the number seventy. If you win, I will by you a drink…and I never buy girls drinks! But if I win, I like a rum and coke

Her: Okay
You: What is 10+10?
Her: 20
You: Multiplied by 4?
Her: 80
You: Plus 60
Her: 140
You: Divided by 10
Her: 14
You: Plus 3
Her: 17
You: Gotcha! I win!!!
Her: No - you said seventy!
You: Now I win
This game works because it plays on one of the fundamental principals of human nature – ego. The girl will want to defend her own ego by reminding you of the rules of the game, and without even thinking about it, says the number that she wasn’t allowed to say.