After that last one it is open season.
See if you can find one worse then this:
To celebrate Halloween, all the math teachers and professors got together for a big costume party. Each dressed up as their favorite math function. One particularly mean and eccentric math professor dressed up as the derivative. He ran up to the teacher dressed as cos(x) and yelled "I derive you!" The teacher tore off his costume and scurried off looking for a -sin(x) costume. The prof ran up to another teacher who was dressed as 4x^5 and yelled "I derive you!" The teacher tore off his costume and went scurrying off, looking for a 20x^4 costume. The prof ran up to a 3rd teacher and screamed "I derive you!" The teacher just stood there with his arms crossed. "Didn't you hear me?! I DERIVE YOU!" he shouted. Again, the teacher stood there, but with a smug expression on his face. "I derive you! I derive you! I derive you!" the professor shouted while jumping up and down. The teacher looked at him and said "derive me all you want. I'm e^x."