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.
