Two chemists walk into a bar, the first asks for some H2O, as he's a chemist. The second says "I'll have some H2O too please. He died.
Alternatively:
Two chemists walk into a bar, the first asks for some H2O, as he's a chemist. The second says "I'll have some water please" The first cries because his assassination attempt failed.
There are 10 kinds of people in this world, those who understand binary, those who don't, and those who weren't expecting a base 3 joke.
What do you get if you cross a mountain climber with a mosquito? You can't, that would be crossing a scalar and a vector.