We blew the domes off a pair of Polk Audio Monitor 10's once. Didn't think it possible, but they were there when we started and on the floor when we were done. All of a sudden there were no highs Weirdest thing I've ever seen happen to a speaker.
On another note, I used to put fuses inline with my speakers years ago because my roommates would tend to push the limits. Only had to replace one mid before I learned that lesson.