The shit stain left on the toilet seat from some fat ass that can't wipe his butt and leaves a mark on the seat for the next guy. Ass lipstick is like the lipstick left on a coffee mug or cigarette butt, except it is on the toilet seat and it is from your ass.
the stain that appears when you havnt had a wash for a good while and sit on the bed and hey presto the chocolate ass lips appear on the sheets!
wife: whats this chocolate on the bed!
reply: it must be the kids again eating chocolate on our bed!
wife lowers her nose to the (chocolate stain) WHAT THE FUCK, THATS SHIT