A man who thinks with his penis instead of his brain. In other words, his actions aren't rational and decisions are totally driven by getting laid.
He has been paying his girlfriend's cable bill so he has an excuse to go over there and spend time with her in hopes of getting laid.. What a dickbrain.
A man, sometimes barbaric or slow-witted, who is particularly gifted at pleasuring a woman. Often, but not always, this is his only redeeming quality and all he has to contribute to a relationship. Other times, it's just a role he plays when called upon.
"Oh, it's not a serious relationship. He's only my dickbringer."
"He's great with the kids and helps around the house, but sometimes I just need him to shut up and be my dickbringer."
When you're typing the greatest comeback of all time, but you start daydreaming about how awesome it's going to be and end up just typing some nonsense.
Dude. That was going to be the sickest burn ever until you dickbrained it.