First spanish game introduced to me by David (thanks for that dude):
-pretty easy to get, but it's as easy to get confused playing it, here is how you play that silly spanish game: you all know the roman numbers yeah? (I II III IV V VI... and so on), in this game every sign has a name: "I" is "puta", "V" is "hijo de puta" and X is "tu puta madre" (do not ask me about 50, you never get there) so when you remember that the game can start: the players form a circle (or something as close to a circle as possible for it can be hard considering the amount of alcohol involved) and the first player starts with "puta" ( I ), then logically the next has to say "puta, puta" ( II ) me sigeis? So 8 will be "hijo de puta, puta, puta, puta", 19 is "tu puta madre, puta, tu puta madre" and it goes on and on until someone fucks up (whether by saying the wrong thing or by hesitating to long), it seems simple I know but when it gets to 5 6 7 8 9 you start getting confused (I've never seen anyone getting to 30).
-another rule which can be added if you still find that too easy is to replace every multiple of seven (7, 14, 21, 28...) and every number endind with seven (17, 27...) you have to say nothing but "pun" (no idea what it means) and the player order goes the other way round...
I think I said about everything you need to know to play this game, if not you know what to do!