Unfortunately, for the University of Idaho, the Vandal nickname was adopted before the term vandal became the common term for someone who damaged property. The average person's lack of knowledge about history also comes into play.
Nonetheless, it's their nickname, and I think it's a great one, though these days the poor Vandals never do much damage to anyone, unless I've missed something.
Wow, in that case the school must be really old because the use of the word vandal as a “willful destroyer of what is beautiful or venerable” goes back to the mid 1600s.