From the (excellent and frankly, as a programmer, terrifying) article on Unix time, the section on time_t, the data structure describing time in a Unix system as the number of seconds since or before midnight 1 Jan 1970 UTC (but only roughly; read the article in full), states:
I’ve been waiting for a thread to mention this, as direct humor in actual wikipedia articles is rare (as opposed to relaying a humorous anecdote or joke):
In the article on the Map-territory relation, there is a caption with an image of Magritte’s The Treachery of Images.
My favorite is not actually a joke, but its absurdist humor is really highlighted by the sheer matter-of-factness with which the information is conveyed. I give you, the opening sentence of the Wikipedia article on General Butt Naked: