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1.
Beer purchased in case you'll need it later. Originated in Chapel Hill circa 2010 (VH)
What's the plan?
I don't know, but let's grab some safety beer just in case
by King of England February 26, 2010
 
2.
The beer that you take to bed with you when you are drunk, to ensure that you have an alcoholic beverage to maintain your current status of happiness and that no one else may take it. This can be consumed while intoxicated, or due to a massive hang over to ease the pain.
CODE RED: WE HAVE NO BEER (EVERYBODY IS DRUNK). But in the back of your mind, you KNOW you have a beer "Safety Beer", and you are OK, You may maintain your buzz as needed.
by timandgeoff December 27, 2013
 
3.
A beer that you drink as soon as you arrive home to prevent you from leaving again, i.e. driving back to work or to pick up a friend at the airport. A safety beer guarantees you a free pass as no one would ask you to drink and drive.
Boss I would love to come back in but I have had a safety beer.

Babe you know if I hadn't already had a safety beer I would pick your mother up at the airport.
by Pseudoname99 August 17, 2013