Similes
The current cartoon at xkcd is inspired by the simile as neglected as the nine button on the microwave. Discussion in their forums reveals that I'm far from the only person to use settings like 0:99 to heat things up.

XKCD is one of my favorite cartoon sites.
One of my favorite similes is: Her grammar was as careless as, well, like, you know ... whatever.

Ha! When I saw the title of this thread I immediately thought of this one:

Heimhenge, even before reading Gödel, Escher, Bach I enjoyed self-referential humor like your grammar simile. Most people enthuse over the Austin Powers movies more than I, but even I laughed aloud at "He has a certain quality, a certain...I don't know what."

Yeah, I've always been a fan of self-referential humor. Read GEB back in the 80s, and I have to say it's one of the top 10 books on my list. When I was teaching, I used to post the usual stuff on my bulletin board, but also had a series of self-referential cartoons that cracked me up, and often garnered puzzled looks from students. Here's a few of them ...