I had a good chuckle. ^^ You call it griefing, I call it awesome tactics. Would have liked to see that.
As to your question - this ain't no WoW, boyo, so it ain't forbidden. I can understand that you feel angry - but this is one of the situations you just have to deal with it - life and such.
They didn't do anything wrong, they played by the rules of the game, you lost. Learn from it and move on.
P.S.: Still laughing. ^^