Integration as a double entendre

I've always been amused at profession- or subject-specific humor. Some of the jokes, such as lawyer or priest or engineer jokes, tend to have a grain of truth, and are amusing to hear. The best ones, though, are those that only make sense to people who have studied a specific field. A couple of examples from my current applied PDEs (for the numerically challenged, that's partial differential equations) class:

When discussing the sifting property of the Dirac Delta function, my professor mentioned, "Well, now you'll ask, what if t0 is at one of the limits of integration? Uhm... well, applied mathematicians like to say that in polite company, we don't discuss that possibility."

(...Which is hilarious if you know about the trouble in defining the Delta function, as heuristic definitions have gaping holes that are inconsistent with normal mathematics, but full definitions are hideously difficult to understand.)

Another one is involving his "motivation" for why we're even bothering to study PDEs (although most of us needed no motivation, seeing as how we've taken some combination of advanced fluids, heat transfer, quantum mechanics, etc.). He said, "So, where do differential equations come from? I suppose this is sort of like teaching sex ed for differential equations." To which I promptly whispered to a classmate, "When two variables love each other very much..."

*chuckles* I'll spare you the rest of the horror that I cooked up in my head, but it used a lot of horrible puns and made-up euphemisms. Math is fun.