A Brainer is when you do something because it had to be done and you knew it was the right thing to do.
1.You gave that guy some of your bone marrow well that's a brainer.
by WolfBrother13le April 24, 2013
when you're excited to learn something new, eg. math, science. it's basically a boner in your brain a.ka brainer.
professor farnsworth: all of this knowledge is giving me a raging brainer!!!
by soma689 April 25, 2013
When you're attracted to somebody primarily based on their personality and mind rather than appearance (although that does help).
"That thing you just said was so cute. I have an erection for you, but in my mind. I have a brainer."
by bobplate May 05, 2014
A word used by senior stagiaires who are trying to look cool. While the validity of the word is contested, it is accepted that the word is not used by anyone anymore, or at least anyone who you would consider to be cool.
Christine: This guy I know went did a degree in engineering and a masters in engineering and now he is in med school doing his residency, what a brainer!

Mat: What's a brainer?
by trusted authority November 18, 2011
Old trainers, where the front has worn down giving the appearance of a throbbing brain.
Haha check out his brainers!
by Lewis1983 May 30, 2005
Not a no-brainer.
His video timer is such a brainer that he is leaving it flashing at 12:00 AM.
by Milt Alwin March 19, 2009
Somone who is smart funny and fun to be around and used to trick people to think ur talking bout giving head
man i love to be around that girl shes a brainer
by gtman43 April 01, 2010
A brainer in when a person inhales marijuana smoke through their nose, sending it straight to the brain.
"Hey man, you wanna toke?"

"No, I'll just take a quick brainer!"
by Kanuckilish March 10, 2009

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