Take turns trying to piss into the toilet. I believe the game goes to round 5.

Every 300 points everyone who is playing takes 1 sip.

Total score at end game < 3000, then drink a beer.
Total score at end game 3000-3500, everyone else take 2 sips.
Total score at end game 3501-4000, everyone else take 3 sips.
Total score at end game 4001-4500, everyone else take 4 sips.
Total score at end game 4501-5500, everyone else take 5 sips.
Total score at end game > 5500, everyone else take 10 sips.

 Click this link via your Wii Browser to play Piss Drunk