Most of these "brogrammer" "frats guy" types that are loathed on HN tend to be a very particular type of person. They were uncool in high school, joined a low tier frat in college and then tied their entire self esteem to their club membership. They remain socially inept after college and therefore cling to their juvenille antics because that's all they know. [0]

In general, the people in the top tier fraternities tend to have extraordinary social skills and meld seemlessly with society after college. You probably wouldn't be able to spot one. As of now, these individuals are very much _not_ in software engineering.

Unfortunately, the top 3 or 5 large fraternities on campus take all the kids with social skills, and the bids trickle down from there. What you're left with is 15 or so fraternities that function as a factory for douchebags with weird personalities. These are the "loser frat guy creeps" that members other fraternities make fun of. Most outsiders are unaware of the social hierarchy within the Greek system and understandy lump everyone together.

If someone is still acting like a "bro" or "frat guy" after college then that's a red flag that they were the social inept guy in their fraternity or in a low tier fraternity.

[0] Source: a few semesters in a Greek Life.