Origin of the word “boner”

Solution 1:

When I was growing up in the 1980s the word "boner" was also used as a synonym for "jerk" or "idiot" among adolescent and pre-pubescent boys.

For example, if your friend was being mean to a little kid or doing something stupid you might say, "Hey, don't be a boner."

"Boner" also means "a blunder or mistake," although that is a more dated use of the word. But its etymology, if you are interested, follows:

"blunder," 1912, baseball slang, probably from bonehead.

Solution 2:

Etymonline has this:

Meaning "erect penis" is 1950s, from earlier bone-on (1940s), probably a variation (with connection notion of "hardness") of hard-on (1893).