1. Annoyingly complicated. DWIM is
incredibly hairy.
2. Incomprehensible. DWIM is
incredibly hairy.
3. Of people, high-powered, authoritative, rare, expert, and/or
incomprehensible. Hard to explain except in context: He knows this
hairy lawyer who says there's nothing to worry about.
See also
hirsute.
There is a theorem in simplicial homology theory which states that
any continuous tangent field on a 2-sphere is null at least in a point.
Mathematically literate hackers tend to associate the term
‘hairy’ with the informal version of this theorem; You
can't comb a hairy ball smooth.
(Previous versions of this entry
associating the above informal statement with the Brouwer fixed-point
theorem were incorrect.)
The adjective ‘long-haired’ is well-attested to have been in slang use among scientists and engineers during the early 1950s; it was equivalent to modern hairy senses 1 and 2, and was very likely ancestral to the hackish use. In fact the noun ‘long-hair’ was at the time used to describe a person satisfying sense 3. Both senses probably passed out of use when long hair was adopted as a signature trait by the 1960s counterculture, leaving hackish hairy as a sort of stunted mutant relic.
In British mainstream use, hairy
means
dangerous
, and consequently, in British programming terms,
hairy
may be used to denote complicated and/or
incomprehensible code, but only if that complexity or incomprehesiveness is
also considered dangerous.