A male, often in (but not restricted to) his late teens to mid twenties, whose most raw state would be what many would consider a "regular dude." On this crude foundation, bros layer an exuberant confidence because of good looks, wit, respect from other bros, success in sports (carnal pursuit being a sport), but more often than not a combination of all of these. This confidence when combined with all of the features that make a bro not "weird" or a "fag", sometimes leads to a prejudice against the lesser "weird" "fags", often vocalized in a bro's boisterous manner.
Most comfortable in social settings with limitless amounts of alcohol (hence the common association to fraternities), and an impressive coherency despite the amount of alcohol consumed. This, in combination with said confidence, has lead bros to exploit glaring insecurities in women, often by putting down and manipulating said women, which is more proof of female stupidity than any given bros demeanor.
A bro's wardrobe is perhaps the most interesting aspect of the creature, as it the most versatile of any other genre of person. There is a notable balance between every category of clothing, save emos, guidos and said "fags”. For example a flat brim(ghetto), throwback John Stockton jersey, nice shorts (preppy), and turf shoes(lax), is a staple broutfit. Not all bros necessarily have this outfit, aspects of even skater, surfer, or even casual luxury apparel withstanding, but girls will stare regardless.
You should have seen Danny's dad at the wedding; he was pounding straight Beam and hitting on all the waitresses while giving his two high school nephews beers. So we iced him and he crushed the bottle, spiked it, flipped the table and blamed the whole thing on the mexican janitor. What a Bro.