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1.
A state, usually precipitated by drinking and drug use, that approaches catatonia. Although common symptoms are indistinguishable from those of a coma, certain individuals may inexplicably maintain random higher brain functions, such as speech, and sexual ardor. May also be used as an adjective or descriptor.
1. Oh man... stay away from Noodles. He's gone brainstem.

2. That stupid brainstem Billy just tried to grab my boobs!

by dayvudd February 12, 2008
 
2.
A term used for people who do not use higher levels of thinking, ergo reference their penis when making decisions.
Guy1:Man I want to smack up that bitch
Guy2:You some kind of Brainstem? fool...

Holy shit, stop humping my leg you Brainstem
by Jeff Wong February 05, 2008
 
3.
used interchangeably with blowjob. See also nerl; scully; blowjob; flowbee.
"I went home with dat bitch from the club last night, and ya know I had to get me some brainstem 'n shit."
by Chirs Bailey December 10, 2003