You will need a large selection of alcohol (Beers, Alcopops, Spirits, Juices etc).
Arrange players to sit in a circle... somebody will need to donate a coin (something like a dime or 2p).
One person starts off by pouring a small amount of a drink of their choice into a pint glass then the next person sitting next to them flips the coin. If they get heads then they have to add something into the glass.
If the player gets tails then they have to down whatever is in the pint glass.
Everybody in the circle could have just had a go at putting a drink into the glass when you get tails so think about what you make other people drink... be nice =)