A homosexual male, who still maintains all the qualities of true bro's. The best example is Neil Patrick Harris.
Friend 1- Wait, so you're saying Esteban played basketball today? I thought he was gay.
Friend 2- He is. He's just an ultimate rainbro.
A group of bro's all wearing different color polo shirts.
Brian and all his friends came over last night in different colored polo's. I could practically taste the rainbro
1. A homosexual bro.
2. The 2007 album by Brodeohead. A Broternative rockband from Brofordshire, England.
1. I'm going to hang out with my Rainbro, but I mean, as friends, ya know?
2. Favorite song of In Rainbros? Got to be Weird Fishes/Broppegi.
The gay guy in the group of straight guys.
Dude 1: Is Patrick your black friend?
Dude 2: No, he's just our rainbro.
A gay black man. A gay brother.
Sista 1 says: That man is FINE!
Sista 2: Girl, redirect. He a rainbro.
One of the guys who is a total bro (usually on a sports team) who takes the "acting gay" thing to far and actually engages in legit homosexual activity with his fellow rainbros.
Dude1: Hey man did you see those football players touchin each other's dicks in the showers?
Dude2: Yea dude they are a bunch of rainbros.