New York Second

The New York Second is a humorous unit of time, defined as the "duration between the traffic lights turning green, and the cab behind you honking". Many believe it to be the shortest unit of time in the multiverse.

Other humorous units include the microcentury (about 52 minutes), the warhol (fifteen minutes of fame, Andy Warhol himself had about 1 megawarhol), and the potrzebie (invented by Donald E. Knuth, equal to the thickness of issue 26 of the Mad magazine). Wikipedia has a list.