The slimy, acrid and bacteria-filled gunk which coagulates and gathers in one's crack.
The heat of the day left its telltale mark of arse paste on his shorts.
To use phlegm as a lubricant while performing anal sex.
Phlegm Sex: I coughed up a loogie and deposited it on Jen's rectum just before I jammed my cock into her arse.
note the colon ;-)