Programmer's day is a whimsical "holiday" on the 256th day of the year celebrated mostly by computer programmers (reason: 256 = 2 to the power of 8 = the number of values representable in a byte of data). Traditions include drinking, behaving silly, coding silly programs, mini computer games, playing with old computers, etc. Programmer's day usually falls on September 13th; on leap years, it is September 12th.
See also: Pi Day