A cat among pigeons

Posted by Joel on May 05, 2002

The metaphoric phrase "a cat among pigeons" refers to an undesirable person from the standpoint of a group. I wonder about similar phrases, but perhaps ones that don't imply the element of aggression (cat vs. pigeon). Does anyone have a phrase or phrases that mean the same thing without a 'power differential' being the key element in the undesirability?