Green’s Dictionary of Slang

punk out v.

[punk n.1 ]

1. [1920s+] (US, also punk) to display cowardice.

2. [1960s+] (US prison) to submit to homosexual anal intercourse.

3. see punk v. (6)

In derivatives

punked out (adj.)

1. [1980s] (US campus) furious.

2. [1980s] describing someone who has been forced to submit to anal penetration.

3. [1980s] in fig. use of sense 2, made to look like a coward; to disrespect.