This isn’t my joke; I read it a long time ago. I paraphrased it below because I don’t remember it exactly. I’m sorry if you don’t understand it and yes I do have a strange sense of humor.

Two mathematicians, mathematician A and B, walk into a bar. Mathematician A says to B, "You know what’s wrong with today's society? No one knows Calculus anymore".

"I'm sure," says mathematician A, "that there are still plenty of people that know Calculus".

Mathematician B goes to the bathroom. Mathematician A makes sure he is gone and then calls over the bartender. "When my friend comes back," he says, "I’m going to ask you a question and I want your response to be x cubed over 3".

The bartender looks confused, but then nods. Mathematician B comes back and mathematician A says, "You know what, I’m going to prove you wrong". He looks at the bartender and says, "Excuse me ma’am, but what is the integral of x squared?"

The bartender looks at him with the same confused expression, but then finally says, "x cubed over 3".

Mathematician A looks surprised, nods, and then says, "I guess I was wrong, people do-"

But then he was cut off as the bartender suddenly stops, turns around, and shouts, "Wrong! The integral of x squared is x cubed over three PLUS the constant of integration!"