Arrange chairs in a big circle. Choose someone from the group to be 'it', and that person stands in the middle of the circle. Have the rest of the group sit on the chairs, and make sure you have one spare chair.
The aim of the game is for people sitting down to prevent the person that is 'it' to take a seat. They do this by shuffling their 'buns' left or right to occupy the empty chair before the person who is 'it' can sit down. Players are only allowed to move left or right (ie. not run across the circle). Eventually once the person who is 'it' gets a seat, the person to their left or right (whoever was slowest) becomes 'it'.
For bigger groups, you may need to have two or three empty seats