ratfink

An informer or spy; a traitor.

The authors have facetiously labeled the contemplated musical as 'Ratfink', after the name of its central character, James J. Ratfink. Its title is not meant in a derogatory sense.

The film director accused him of being the worst kind of a rat fink (rat pack talk) for leaving a play so early.

A dislikable or contemptible person.

Maxwell—or Maxie, as he was familiarly called by his once and former rat fink girlfriend—lived in a six-story walkup on a narrow street in Calm's Point, […]

He [Dubyaman, a parody comic superhero based loosely on George W. Bush] searches for "dirty ratfink terrorists" and aims to ferret out their "whacko ideas."

A strikebreaker.

To inform on; to betray.

It led to some rather incredible and colourful claims in the submission by the union that the employers had ratfinked on previous agreements.

The dumb bastard says he never rat-finks on a woman. They're too precious, he tells me. And he should know. He has had many of them.