What is Spy's Sappin' Mah Sentry!?
1.
In the popular multiplayer shooter Team Fortress 2(tm) made by Valve(tm), spies are a nuisance. They run around, backstabs players and disguises as players. But above all else, they are SAPPIN' MAH SENTRY!
An engineer builds stuff. A spy saps the stuff the engineer builds, and utterly destroys it in a matter of seconds. Naturally, they are really annoying. The engineer thinks so as well. That's why he yells out "Spy's sappin' mah sentry" in pure fear and helplessness.
Also the inspiration to "spy's a spy!", created using digital soundboards.
The phrase is mostly used to describe a sense of fear, despair or pure hate when someone completely ruins whatever you're trying to accomplish.
For the love of God, SPY'S SAPPIN' MAH SENTRY!
See