A female's upper lip that resembles a smear of fecal matter caused by excessive waxing and exposure to the sun.
Lauren Conrad's upper lip on Season 4 of the Hills is a perfect example of Poo Lip.
Someone has poo lip if they have accidently wiped resin from the end of a half smoked spliff on there lips. The sticky brown substance resembles faeces and a ganj-naive associate may believe you've been giving someone a rim job.
Joseph: "I'm going home now.. Gotta be up early tomorrow"
Deano: "You better wipe your lips bro, that poo lip might leave your mum thinking you've been doing a bit of butt munching"