Shamelessly lifted from reddit:
Pavlov is sitting at a pub enjoying a pint, when he hears a bell ring. He jumps up shouting “oh shit, I forgot to feed the dog!”
Another one-liner:
One hundred thousand Pascals go into a bar. (Conversion complete)
And talking about Pascals:
Einstein, Newton and Pascal are playing hide and go seek. It is Einstein’s turn to count.
As Einstein starts counting, Pascal runs to hide. But, Newton very calmly picks up a stick and scratches a perfect square, 1 meter per side, in the dirt – and then stands in the middle of the meter square.
Einstein finishes counting, opens his eyes, turns around, sees Newton standing there and calls out: ‘Pascal, I’ve found you!”
Xanthippa's Chamberpot 