The way this game works is every time the word f**k is used (in any form, ex. f**king, f**ker, etc.), or the word dude (in any form, ex. "his dudeliness, the dudester, etc.) is used, you take a drink. If you've seen the movie, you'll know that after five minutes of playing, you should be dialing 9-1-1. The main character's name is "Dude" and swearing, especially with the f-word, is quite excessive. Because both dude and f**k are used so much during the movie that we altered the rules to include that you can choose to only drink when one or the other word is said.
I can promise you this: Playing this game makes the movie make a lot more sense.