There's a spectrum of bro-ness, and I've seen pretty hardcore stereotypical "frat guys" at 22 mature into "normal" adult human beings on a regular basis.
If you can keep your bro-ness under wraps for 4 hours for the interview, you can get hired at a company with a reasonable culture and that will continue to mold and shape you, just like any other community influence to which you are consistently exposed.
Why is it someone else's job to "un-bro" them? Why can't it be their job to do it for themselves, and just have them find out they're unemployable in their desired job unless/until they do? Companies insist they won't hire people who'd need to learn other fundamental skills of the job (and that if you want the job, learn that stuff first), so why not this?
If you can keep your bro-ness under wraps for 4 hours for the interview, you can get hired at a company with a reasonable culture and that will continue to mold and shape you, just like any other community influence to which you are consistently exposed.