A woman (or possibly a man) who will talk to a guy at a bar, flirting and giggling and what-not, because they are either trying to score free drinks (consciously or subconsciously) or are so insecure that they believe talking to a guy they would normally never sleep with and taking their free drinks is a good esteem booster. Generally the drink slut is the one that says the Jonah Hill quote "I got so drunk last night, I shouldn't have slept with that guy." To sum it up, the drink slut is a deceptive con artist that uses men.
Guy to another guy: "Dude last night, that chick I was pumping drinks into had no idea how hot she is."
Other guy: "Nah man, she knew, she was a drink slut."