Recently, it's come to my attention that I'm an old fart who doesn't find things funny that a lot of other people do. I like to think that there are probably other things that I do find funny which others don't, to kinda balance things out, but maybe not. I do tend to be a rather serious guy, but it's not like I don't enjoy a good laugh. It just has to actually be funny, to me.
Everyone finds different things funny, and over the years, people have tried to determine exactly what makes something funny. Also, a combination of circumstances and stuff like the mood you're in can make a big difference. Something you find hilarious today might just be annoying tomorrow. Some things are funny every time, others stop being funny after a few times.
My conclusion is that the root of humor is conflict. Something wrong (a conflict between good and bad) or something unexpected (a conflict between what you think should happen and what does happen).
Someone once said that pain is required. No. Someone getting hurt is only one kind of humor and it's usually not funny at all. You might laugh at someone falling down, or saying something really serious and then turning and walking into a wall. That kind of thing. But you're not laughing because they got hurt; you're laughing because what happened was unexpected. There was a shock and you had to release it.
Consider satire. No pain or suffering required. Saturday Night Live. Monty Python's Flying Circus. In a completely serious setting, people are doing what you'd expect them to do, then something absurd happens because this is satire. It's funny because there's a conflict between what you expect and what you get.
Again, these are just examples. No two people laugh at the same things, and no one person finds the same thing funny all the time.
Now consider the phenomenon of tickling. Most people find it at least mildly amusing, or downright funny, but some hate it. It is a mock attack, a physical assault, but instead of pain being inflicted, there's just a minor stimulation. Usually tickling is accompanied by a mock aggressive stance. This creates a conflict in your brain. Your defenses are instinctively triggered, you tense up, but no actual pain is forthcoming, resulting in a physiological response that's just plain confused. Strange how laughter looks like crying with no sound. It's all tied together. Laughter and crying are more similar than you'd think. Both are forms of emotional release, and extreme cases of each can lead to the other. Ever laughed so hard that you cried actual tears? Most people have. And when things are bad, really bad, have you ever laughed? Nothing left to do, crying won't help, so you laugh instead.
So now, the part you've all been waiting for, which is when I explain why there are certain things I just don't find funny that others apparently do. Being mean to someone for no reason. It's unexpected, and if it's cleverly done, then I can see why people find it funny. It meets all the criteria that I just spent ten minutes outlining. But why it doesn't work for me is because someone has been hurt. Maybe not physically, maybe just their feelings. If my empathy for the victim outweighs my shock at the conflict, it's just not funny to me. Yep, what you said was witty, you sure told her, you and your friends got a good laugh out of it, but she's not laughing. She just thinks you're an asshole for saying that, and I have to agree. Humor does not need to be at the expense of others. Maybe after a few beers, I'd have found it funny too. Maybe the whole world is just normally a few beers looser than me.