people who make up ridiculous stories simply because they don't have anything interesting to add to a conversation. so instead of commenting on someone else's story, or simply saying nothing, they decide to make something up and it's ALWAYS something that's just a little bit "better".
example:
Person A: "yeah man I got locked up this weekend for possession, I got a good lawyer though so I should be ok"
Person B: "aww dude that sucks, I hope it works out for you"
Person C (bullshitter): "oh man that's NOTHIN' this one time I got busted with 2lbs of KB and a half a Kilo of COKE! Yeah but my lawyer knew the judge so they let me off with just a warning"
Its the worst when you work with this person, because you can't escape the bullshit stories for 8 hours a day, and no matter what you talk about, the bullshitter will have a ridiculous story to tell that may or may not have anything to do with the topic at hand.