infinite mathematicians enter a bar. the first orders a pint of beer, the second orders half a pint. the third orders a quarter pint, and the bartender cuts them off there and just pours them two pints
after a time the mathematicians indicate they're ready for another round. as before, the first one orders a pint and the second orders a half. when the third orders a third of a pint the bartender says "actually i think you've all had enough for tonight"
infinite mathematicians are in a bar, nursing epsilons of beer from a previous order and getting a bit mischievous. catching the bartender's attention, the first orders a pint. the second orders two pints, the third three pints and so on. after a while the exasperated bartender pours a twelfth of a pint out of the mathematicians' glasses, at which point a brawl breaks out
explaining the joke
@Efi the divergent series 1+2+3+4+... and the number -1/12 appear together in a couple of interesting contexts: https://en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E2%8B%AF
