A muddy gumboot is when a drink is poured across the anus and butt cheeks of the server while the receiver lies underneath and drinks the liquid.
Usually done with alcohol during drinking games. But can be done with other liquids.
Thought to have originated from Massey University in New Zealand.
If a player vomits or urinates they have to drink it, or get someone else to, through a funnel or muddy gumboot.