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1.
A term to describe a unplanned and sometimes sudden drinking session entered into while on ether a "casual lunch" or during "work lunch".

This occasion is mostly accompanied by the quote of the Alan Jackson song "It's Five O' Clock Somewhere"
person - screw this job im gona go get drunk
workmate - Drunk Lunch?
person - yep
workmate - ow hell it's five o' clock somewhere
by cheeky bull January 20, 2012