That acronym stands for "Bastard Operator From Hell".
The following links are much funnier if you are A) a nerd and B) have a fairly decent concept of UNIX and its administration. However, these are not necessary.
Also note that I am gullible, and at first believed these things. That was until the "accidents" started.
The first link is the early work, the second link is to the current site of the BOFH.