underdecking 

conspiring against an authority figure to take synchronized shits underneath said authority figure's deck. Usually performed in groups of two to five people. In extreme cases, shit burritos are fashioned with paper towels and left to be found.

Oh, no. Have you seen the kids? I hope their not underdecking us again!

underdecking by underdecked July 2, 2009

Undiefucking 

The act of dry humping in ones undies is called Undiefucking.

John found Audrey undiefucking another man in her fishnet undies.

Undiefucking by Nathan Eastan October 10, 2007

Cuban Underduck 

When you bend your dick down and back, and a girl blows you from behind with her nose on your butt hole.

"I got a dandy Cuban Underduck from the broad I met at the bar last night."

Cuban Underduck by TurdFerguson21 June 3, 2016

underfuckingstand 

underfuckingstand - Understand, with "Fucking" inserted in the middle, making it an exclamation of frustration or, in some cases, a joking statement.

"What part of this do you not underfuckingstand?!?" or "I dont underfuckingstand!"

underfuckingstand by Steve October 24, 2004

undercock

The male genitalia being viewed from an upward looking angle. Similar to the female version of underboob but with a wiener instead. Also referred to as Australian dick.

I knew I was going to have a rough day when I woke up to my roommate giving me some undercock.

Your mom seemed pretty interested in me so I gave her a little Australian dick.

undercock by nubforce November 26, 2010

Dunderfuck 

When "stupid motherfucker" just isn't enough. A person of unlimited stupidity.

Linkin Park is not metal, you fucking asshole. God, you're such a dunderfuck.

Dunderfuck by Ken April 19, 2003

Unbefuckinglievable 

Like unbelievable, but with a swear to kick it up a notch for people who just can't believe what just happened.

"Unbefuckinglievable," Jan said, after getting another term paper that week.

Unbefuckinglievable by Ashleybobashley xD January 20, 2009