Crazyass Anime

[Idol]

I thought there was plenty of random insanity in Azumanga Daioh. Great humor paired with interesting characters.

Other suggestions not mentioned before:

Magical Shopping Arcade Abenobashi (persiflage galore)
Cromartie High School (crazy stereotypes in an undisclosed plot)
Hare + Guu (rumble in the jungle)
Kekko Kamen (hilarious classic)
Child's Toy/ Kodomo no Omocha (random fun with Sana-chan)
Cat Soup (not hilarious but definately insane)
Dead Leaves (total mayhem)
DiGi Charat (the original 16 ep series, not the other ones)
Animation Runner Kuromi 1+2 (not that random but still funny as hell)

... and maybe some episodes of His and Her Circumstances/ Kare Kano.