I pulled a boner, he pulled a boner, she pulled a boner, they pulled a boner

Coined in 1896, the expression has been co-opted from its original meaning: I made a mistake, I blundered, I fucked up, to the arousal state of a male’s penis. Any etymologists out there who can enlighten us as to how the word boner came to signify both a mistake and a stiff dick? Same thing happened to the word gay. All lyrics containing that word become double entendres: “I use to visit all the many gay places, those come what may places,” I’ll be seeing you in everything that’s light and gay, I’ll always think of you that way,” "but I feel so gay in a melancholy way, that it might as well bu spring,” “I feel pretty, oh so pretty, I feel pretty and witty and gay,” “don we now our gay apparel, fa la la la, la la la,” “Then gay youth was mine, truth was mine, joyous free and flaming life forsooth was mine……where does it stop? And why have we stopped using the expression I pulled a boner???