What hurts a speaker?

I have never really been clear on what hurts a speaker. Will the popping sound on vinyl hurt speakers? What about distorted material i.e. track 9 on Bjork's Homogenic album? This song contains digital distortion.
What doest hurt a speaker?
too little power
Power amp and kids.
From your amp or receiver's perspectives ... mostly "dirty" power will damage speakers. Said differently, running your amp to the point where it begins to clip/break-up, will damage your speakers.
Here is a rule of thumb: if you regularly drive your system into distortion, eventually it will break.

Most commonly, pushing an underpowered amp to the point of distortion causes excessive heat inside the tweeters. The heat melts the tiny wires in the speaker windings to the point they act like a blown fuse and short out. Driving woofers into distortion can misalign their suspensions. Constant abuse can tear them apart. If a woofer cone has jumped out of the gap it lives in, sometimes you can reseat it by hand and everything will be ok.

The occasional pop is probably ok. I doubt any recorded distortion will hurt them, so long as the distortion is reproduced cleanly :^)
Playing any LP or CD by "Chicago"!

You said it brother! Those nice, shiny round things that are at about eye level are extremely tempting for young kids to poke.

Yawning and falling asleep is very insulting to a speaker. Also having a conversation with someone can also be a bit offensive to a speaker. Showing up late, and/or leaving before the speaker finishes is rude to a speaker. And never mock or make fun of a speaker.
You are most likely to notice a problem with your speaker after getting a demo of your buddy's new kilobuck set up.
This can be corrected by spending an equal amount of money yourself.
A chain saw.
Being mentioned in the same sentence as Bose.
Rosstaman makes excellent points! You should also never mention in front of a speaker that it lacks bass or does not image well. Do not compare monitors to full range speakers - in extreme cases they have been known to cry. Also (very important) NEVER mention - even in passing - that you would like to try an electrostatic speaker when in earshot of a dynamic speaker or vice-versa. This is extremely gauche behaviour!
Really offended speakers have been known to get even by eating the output devices of your favorite power amp or intentionally smearing vocals and string instruments. Speakers are also capable in extreme cases of transmitting subliminal messages to new/prospective dating candidates - Ya don't want your speakers hinting to the new girlfriend that your have crabs, DO YA?

Be nice to your speakers and they will in turn be nice to you.
A recent and real story: Fired up the amp only to jump backwards at a deafening and startling sound. The 1.5 yr. old had adjusted the volume (to the top) and switched the tuner on. The woofer seals both split. Fortunately, it was the cheap (relatively) basement system!
Esteemed gentlepeople. What has always hurt any speaker most is no one listening (OK, horns excepted). Otherwise, pandering to the turntable is especially egregious.
Getting into an argument with the girlfriend over the phone, losing your tempter and throwing the phone....
through the speaker..

Also on the list..
Flame Throwers
Falls from any great height
Spitting Llamas
heroine needles.
Rap Music!!!!! :)