Green’s Dictionary of Slang

boner n.3

[SE bone of contention]

1. [1910s+] (US) a serious mistake; esp. in phr. pull a boner

2. [1960s] (US campus) a difficult examination.

In phrases

pull a boner (v.) (also …bone, …bonehead)

[1910s–80s] (US) to make a (serious) mistake.