A really sloppy, annoying, and usually slightly overweight sorority girl. She's most likely the black sheep of the group. This girl will be the most drunk, the most forward, and the most not attractive.
I hung out with Jess and her friends last night, but I had to leave because that swampdonkey friend of hers was all over me.
Although it is typically used as a noun, ie "she's a swampdonkey" (referring to a particularly nastyfemale) it can also be used as an exclamation of immunity. If a male and his peers go to a social function, one male from the group is allowed to claim "swampdonkey". This allows said male to take home even the dirtiest of barflies home with him while his mates are not allowed to give him a hard time of any kind. This is typically used when a male is on an extended dry spell.
"Hey dude, remember that nastychick you went home with last night?"
"Hey, shut your suckhole, dude, I called Swampdonkey".
A nasty, smelly, beast-like whore who looks like the sister of the star of 80's film classic "The Swampthing". Panic and heavy drinking always follows awakening next to this gnarly, cum-gurgling creature that is a carrier of several unknown venerial diseases.
After thowin back 16 foties of OE the night before, Tay-Tay awoke next to a swampmonster and a rashy crank.