The act of slapping one's lips and tongue in order to make a random, annoying ass noise to fill in awkward gaps, when really, one is only making them more intolerable. It is fairly similar to chewing with your mouth open, without there being any food in that annoying ass suck-hole of yours, which should just stay closed all the time. Often it is done randomly, and cow-like to maximize its effectiveness.
Douche: *random tongue clapping noises*
You: Goddam Kerwin over here won't stopping his lip clapping and I have a severe case of wanting to punch him in the suckhole.