It refers to the (unfortunately named) "Bro" subculture

https://en.wikipedia.org/wiki/Bro_(subculture)

>Bro is a subculture of young men who spend time partying with others like themselves.[1] Although the popular image of bro lifestyle is associated with sports apparel and fraternities, it lacks a consistent definition. Most aspects vary regionally such as in California where it overlaps with surf culture.[2] Oxford Dictionaries have noted that bros frequently self-identify with neologisms containing the word "bro" as a prefix or suffix.[1] In a New York Magazine article in September 2013, Ann Friedman wrote: "Bro once meant something specific: a self-absorbed young white guy in board shorts with a taste for cheap beer. But it’s become a shorthand for the sort of privileged ignorance that thrives in groups dominated by wealthy, white, straight men."[3]

It seems advertising on crap sites with annoying blog spam is dominated by males, and I say that as a male who has considered doing that for my startup. I don't know if it's unique to men or if it's just because there seems to be more men than women founders, but that's the impression I get.

When I see a startup with a woman at the helm, it seems that advertising is a bit less aggressive, but again, that may be selection bias.