The participants in the thread give some of their favorite examples of, er, striking index categories, but they fail to note one of the ur-examples of snarky indexing, the indices of The Spectator. This proto-blog has some of the most provocative index categories I've ever read; I need to figure out exactly when they date from, as the latest edition I've so far consulted goes back only to the 1790s (the Spectator started publication in the 1710s). I'd comment on Crooked Timber, but the post was in 2003.
Some examples (from a handy 8 volumes in one edition from Philadelphia's Hickman and Hazzard, 1822):
--Bawdy-Houses frequented by wise men, not out of wantonness but strategm
--Biting, a kind of mongrel wit described and exploded by the Spectator
--Crazy, a man thought so by reading Milton aloud [not cross-listed under Milton]
--Drums, customary, but very improper instruments in a marriage concert
--Gentry of England, generally speaking, in debt
--Heads never being the wiser for being bald
--Marriage, always a vexatious or happy condition
--Politicians, the mischief they do
--Some at the Royal Exchange [That is the full listing under Politicians]
--Thinking aloud, what [A particularly bloggy title, I think]
--Women: Not to be considered merely as objects of sight
--Women: Signs of their improvement under the Spectator's hand
It should be noted that when you go to the specific entry, the argument suggested by the index might get to a paragraph's length, out of a letter of maybe six pages.