When you go swimming and you can't change out of your swimwear right away.
When your butt is like in a pool of sweat or is very sweaty
When your ass sweats so much it becomes a viable option for Shrek to relocate to.
"Did you see his swamp ass?"
"No."
"He had swamp ass, and I want to eat it."
A person who suffers from sweating form the buttocks due to playing a video game form 4am till 10pm
Damn Zay when you stood up all i saw was swamp ass from your bean bag and your ass.
When you hold in a poop in a car with the seat heater on and your poop starts to water down and it runs down your butt.
"OH SHIT SON IM STARTING TO GET SWAMP ASS"
When it’s hot and you’ve been sat down for ages causing your bum to sweat lots
person 1: “Hey I’ve been gaming for hours and my bum is wet”
Person 2: “You my friend have got something called swamp ass”