That erection heterosexual men get when
A:observing and/or participating in feats of extreme manliness
or
B: while doing or seeing something extremelyBromantic.
A: Hey man, Turn off the wrestling, it's giving me a broner.
When Two dudes are talking about chicks they have fucked and the dude who is listening to the story gets a boner.
Johnson: the other day i space docked this richously hot bitch at some frat party there was mad poop on her vag.
Steve: no fuckin way that just gave me a ragging broner.
A broner is the excitement a man receives when he's informed of a bro related event that the man is eager to experience. When a man gets a broner, he is not erect it is merely a metaphor for excitement.
A completely non gay experience in which one bro observes another bro having an erection. Following the experience, the observing bro may follow with "congrats on the broner, bro."