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1.
When a girl gives a blowjob to more then one guy at the same time. The girl is the locomotive pulling the other cars of the train. thus called a brian train.
"last night we had a brain train going with this girl.. she was blowing all three of us at the same time!"
by conduct0r August 22, 2009
 
2.
It's your train of thought, which all goes to naught if what you end up with isn't what you sought.
"Shit yo, your brain train just derailed! That shit ain't germane to ANY topic" - said to someone whose conversation went from sleeping bags to whether it would hurt to be slapped in the face with a dick
by Techno Dracula January 28, 2009
 
3.
The long (or short) line of guys you have given head to in the past. Each new guy is in turn added to the brain train, the last guy being the caboose.
That's one guy I definitely want on my brain train!
by Karl Van October 13, 2010
 
4.
THE ACT OF PENILE INSERTION THROUGH ONES NASAL CAVITY.
YO, ME AND MY HOMIES DONE RAN DA BRAINTRAIN ON DAT BITCH
by JACKRAT August 02, 2008
 
5.
To Brain Train someone is to "school" them, or "shut them down" with a direct factual comment, sometimes with the help of sarcasm, (but not always) that renders them speechless.
Dude 1 Says: I think my rotor's need replaced because everytime i start my car it squeals.
Dude 2 Says: (with sarcasm) Yeah...Because that wouldn't be your belts needing replaced.
Dude 3 Says: He just totally Brain Trained you!
by *V3R!T@S* April 19, 2010
 
6.
A group of attractive females travelling all places together, generally with one less attractive one to further their own appaearances; see Brain, sloth, and sloth caboose.
"oh man, looks like a brain train is rolling into our station."
by Rob Engle August 28, 2005