The Monster mash 

When a person has a bowel movement while showering and proceeds to force it down the drain with his/her foot.

I could tell from her glistening brown toes that Ethel had done the monster mash this morning.

The Monster mash by Stinner July 6, 2018

the horizontal monster mash 

sex with a chick... fucking a chick, banging a chick.. that sort of thing

omfg! Their doing the Horizontal Monster Mash on my leg!!! (WTF?)

the horizontal monster mash by teh_n00berx0r June 12, 2006

The Michigan Monster Mash 

The Michigan Monster Mash happens once a year on Halloween night. It is a event where many people at a Halloween party get together in costumes and have a mass orgy. The best part of the Michigan Monster Mash is that everyone is in a costumes and no one knows who is who. So next Halloween go to a local part and do the mash ;)

The Michigan Monster Mash happened in Ann Arbor Michigan on Halloween night in 1999, and has happened ever year since.

The Michigan Monster Mash by DR124 September 19, 2011