‘Brolic ahh dih’ is a play on words, simply referring to not just a big dick, but a substantially strong, veiny, muscular dick (hence the use of the all encompassing synonm ‘brolic’).
The term/phrase (and others similar) were cultivated though out social media
meme pages, most commonly found on memes targeting and ridiculing the transgender and queer ‘son’ of basketball star Dwayne Wade. His
child, Zaya Wade, would naturally be suspected to partake in
homosexual activities, a commonly ridiculed activity, hence the memes uprise.