What is Mississippi Mud Slide?
1.
an act which enlists a group of posh, pretentious twats, who, usually, know each other from the villages' local cricket teams. Said twats get naked, and all do a shit on a long peice of heavy duty plastic which is laid out down the length of one's garden. They then proceed to take turns in running up to and sliding down the plastic, which by now is covered in shit.
posh twat 1: "oh Mortimer, do join us for a Mississippi Mud Slide on Saturday after cricket."
posh twat 2 (who we now know as 'Mortimer'):"That'd be just splendid if I didn't have an infected bock boil. I'll come along for the chinwag though"
See
2.
To freeze a piece of shit and roger your partner with it. As it melts the poo will slide down her/his legs.
When she awoke I told her that she had left a candy bar in her ass crack by mistake; I was ashamed to admit I had given her the Mississippi Mud Slide while she was sleeping.