Unicycle Polo was a sport invented by Dave Lister as one of the "ingenious ways of wasting time" aboard Red Dwarf. Lister often played it with Cat on Floor 14. The game involved belting a beach ball up and down the corridor with French loaves of bread, whilst riding unicycles.
When Lister became depressed at his life aboard Red Dwarf, Unicycle Polo was one of the games Cat tried to get Lister to play to cheer him up. However, Lister then said it was stupid and puerile and he didn't want to play it anymore. ("Timeslides", Series III)