To avoid, at all cost, any situation that might remotely result in a failure on your, and your liabilities, part.
Example 1:
Stan: "Hey man, let's go to the mall, I want to get something to eat."
Sami: "Nah man, you're only hungry because you have post-high munchies. We should wait at my house before we go out anywhere. Plus, I have some Doritos at home you can munch on."
Stan: "Sweet, failsafe."
Example 2:
Sami: "Hey Charlie, can me and my girlfriend skip school at your house?"
Charlie: "Sure, but you'll have to leave before 12, my mother might come home early for lunch. Gotta be failsafe man."
A term derived from shakespearean name "falstaff", who is generally identified as a drunkard and a coxcomb. Can be used as an insult if you are among friends who have read the Henriad.
When a magnitude of a problem as a consequence of an action goes beyond a simple mistake, it is otherwise known as a failstake. However, failstakes rank under the degree of epic fail.
"I tried to wipe Mr. Krabby's first dollar with your tie and ended up covering the whole thing with paint by mistake."