A person who makes out with people indiscriminately. Caliber of victim normally doesn't factor in and therefore can be quite low. Doesn't usually take it past second base tig ol' bitties. Tend to not care about their conquests.
"Liam is a lip slut, he pulled Alison's friend and called Amber to come over that night."
"Damn dat bitch be uuglay fugly, she needs to get with a lip slut"