A slipper and subtle knave, a finder of occasions, that has an eye can stamp and counterfeit advantages, though true advantage never present itself; a devilish knave.
– William Shakespeare
Othello, Act 2, Scene 1. Iago tells Roderigo that Cassio is a crafty rogue who is on the lookout for sexual opportunities and will take advantage of them. He is suggesting that Cassio would bed Desdemona if given the chance. It’s rather ironic for Iago to describe Cassio as a "devilish knave," since it is a description better fitted to Iago himself. His hatred for Cassio comes through loudly in this description.