1. a guy who sleeps with and/or dates a lot of women, usually unbeknownst to potential victims--at least until a certain point.
2. a guy who charms women into thinking he is into them and knowingly or unknowingly breaks their hearts when he is "kinda a thing" with someone (most likely just for fucking) and also fits the first definition.
3. a guy who is even more apt to fit the above definitions when he is in some sort of "relationship" but uses terms such as he is "kinda a thing" with her, and other people say "he has been seeing someone recently," and still remains single on Facebook. This makes it clear that they are not actually "dating" and they are probably just fuck buddies.
See also: player
He charmed me so I thought he was into me, but then I asked him to a ball and he said he was already going with someone who he was "kinda a thing" with...what a womanizer!
I can't wait until he realizes what he could have had--he still wants to be friends but honestly I don't know...that womanizer. He seems like a good friend but it's possible he is still trying to womanize