Informal slang meaning crazy, wild, or behaving strangely; also can mean resembling or related to a wig.
From 'wig', originally short for 'periwig' (17th century). The slang meaning developed in mid-20th century American English, possibly from 'going wiggy' as going off one's head.
The slang 'wiggy' probably connects to 'going wig' or losing your hairpiece as a metaphor for losing your mind—a funny example of how physical appearance becomes code for mental states in slang.
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