Little brain 

Slang for penis, particularly when is not thinking rationally, but mostly due to hormonal motives

Stop using your little brain to think and get it together.

Little brain by danglyballzjohn December 26, 2021

beat the brains out of the little soldier 

To jerk-off purely out of sheer sexual frustration or desperation.

"Man, that ho at the club was grinding on me for like two hours, then she left with my friggin' roommate! I gotta' go beat the brains out of the little soldier!!!"

beat the brains out of the little soldier by richard vendor October 22, 2012