businessdictionary.com:

Dirty hands doctrine. Legal principle that a participant in a wrongful act may not recover damages resulting from it (may not sue the other participants in the wrongful act). Also called unclean hands doctrine.

Example. If A uploads mislabeled files to a peer-to-peer network, and B, C, D participate in sharing that file, although sharing per se may be illegal, A cannot sue B, C, and D to recover damages.