undorphins 

A negative feeling after a major workout, whether it is being tired, exhausted, depressed, etc. The opposite of endorphins.

After going for a run, I felt exhausted with pain coursing through my body, followed by feeling tired. Why did I have so many undorphins?

undorphins by JoltIR0N April 9, 2019

Undermindtm 

A clothing and accessory company started by Matthew Vargas in Morgan Hill, CA. Established in 2004, the company makes a wide range of products marketed mainly to the LGBT community.

Guy 1: That's a cute shirt man.

Guy 2: Thanks, I got it from Undermindtm, bro.

Guy 1: Let's make out.

Undermindtm by NickFirato October 19, 2011

Wailing underpants

Activities in the underwear that demand immediate attention either sexual or toilet related.

Palmer had to go to the toilet quickly due to his wailing underpants!

Wailing underpants by I, Wreckerrr October 30, 2016

Underpants journalist 

A journalist who writes about and/or dressed in their underpants. Often referring to bloggers or freelancers who work from home/their parents' basement.

"TMZ may have broken the 'Michael Jackson is dead' story, but they're still a bunch of underpants journalists."

Underpants journalist by Stable of Crayons July 21, 2009

underminiac 

Noun. A word blend of undermine and maniac. Depicts someone who cannot help them self from making undermining comments. As with kleptomania the underminiac is largely unconscious of this behavior even though it might seem like they take sadistic gratification from it. Their victims are often left realizing how badly they were trashed for days and weeks afterward as many of the undermining comments are not initially obvious.

Lunch with that underminiac will leave your ego in a coma for weeks afterwards.

underminiac by Swampybaby January 6, 2017

Underpants Gnomes 

From the TV show South Park. They steal underpants in order to make profit. They even educate children on how profit works. Here's how:
Stage One: Steal Underpants
Stage Two: ???????
Stage Three: Profit!

The underpants gnomes robbed my house again.

Underpants Gnomes by funwillfunwill June 20, 2015

raving underpass

The act of dancing underneath a concrete structure, to any given beat. Usual participants are gothic warriors and princesses.

Buddy and Joe were raving underpass I-95 over the weekend.

raving underpass by WebstersBest June 8, 2016