A Muslim bro- the "Omar" part references the Muslim Umar, which, in Islamic culture, means first-born son. The "bro" part is self-explanatory.
This phrase can also apply to many southern Italians and Sicilians, who are more likely to drink and bro out.
Hey bro, we got any Bromars in this year's pledge class?
Yeah. He's a Bromar alright, but don't be fooled. He drinks like a fish.