What is Check Valve?
1.
Used to describe a selfish person. Commonly used by navy machinists. If a person goes to a vending machine and doesn't ask anyone if they want anything.
"Hey shipmate, how's the soda?" Thank's for not asking me if I want anything. Fuckin' check valve."
"Hey look at that nub over there eating McDonald's. I'm not signing that check valves qual card."
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2.
A person who does not have the capability of seeing both sides of an arguement.
Following an arguement where the one person continues to not recognize that his/her point of view could not possibly be incorrect.... "Why cant you at a minimum see that the other side of the arguement could have some merit? You fucking check valve. You one way mother fucker!"
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