Green’s Dictionary of Slang

1. a fool.

1608		Dekker Lanthorne and Candle-Light Ch. 2: A Foyst nor a Nip shall not walke into a Fayre or a Play-house, but euery cracke will cry looke to your Purses.
1640		The Wandering Jew 40: Who is this Ioculo? A melancholy Hee-Cat (sir) said the cracke.
1703		Apollo’s Feast 24: Will, as arch a crack as any in this Town.
a.1719		J. Addison quoted in Annandale n.p.: I cannot get the Parliament to listen to me, who look upon me as a crack [F&H].
1997–2000		Da Bomb 🌐 7: Crack: Nutcase; a person who lacks good judgment.

2. (Aus.) a prostitute’s client.

1983

R. Perkins Drag Queen Scene 107: The girls generally have a low opinion of the men who seek out prostitutes, as is seen by the terms they give them, like ‘mugs’, ‘cracks’ and ‘gutter-crawlers’ [Simes:DLSS].