This week's cultural tips come from the Grade 6 lesson: I'm Stronger Than You. This week's topic: Cultural Gestures.
Thumb up: it means 'OK(agreement, permission)', 'number one', 'president', 'best', etc.
Thumb down: it means 'negation', 'objection', 'kill', etc. This has originated from the Roman gladiators' match in which the lost gladiator's life was up to whether the audiences held their thumbs up or down.
I'm going to go out on a cultural limb and say that thumbs up most certainly does not mean president, although 'Thumbs Up Obama' does have a nice ring to it. I've also never intended to kill anyone by flashing the tumbs down. Both of these interpretations make the game Heads Up Seven Up a little more interesting though.