"My penis is throbbing" is a funny post, because it's inappropriate to and random, to talk about such a thing.
An alternative version of this joke would be "My clitoris is throbbing", and this is also funny for the same reasons above, but it has added humor because a person with a clitoris would be even less expected to be so cavalier about their arousal, due to gender norms in our society.
Even the nature of me explaining humor so dryly is, in my opinion, funny. Because it is unexpected, one does not expect humor to be discussed clinically. Funny.
And so "funny" is pretty much "the unexpected", that's pretty much what all humor has in common, it's either an unexpected situation or an unexpected outcome, but that's pretty much it. Some jokes have anticipation, but not all. Some jokes have no set up. You can glance away from your speaking partner and see a man fall on ice in a funny way out of context and laugh your ass off, that had no set up. Funny is just unexpected shit happening, but not just that, it's unexpected shit that for lack of a better word "resonates" with you. I know that's a pretty shitass explanation, but that's why humor is personal taste. It's not funny to see your loved one obliterated in a burst of mist, but if you saw your most hated enemy at war get blown up in an unexpected way, you'd laugh your ass off and cheer. Humor is subjective, but it has one thing in common between all of us, it always involves a little surprise.
