Shortened form of the word martyrdom, used in the Xbox 360 and PC game Call of Duty 4 to express disgust for the use of the "martyrdom perk" in which a downed enemy drops a live grenade upon death, often catching the unwitting killer in the blast. Players often whine about this game mechanic as unfair but are usually quickly met with the counter argument that it is indeed part of the game and that if they cannot handle COD4, they should go play World of Warcraft.
"Ha! You walked right over my marty grenade!"
"Damn marty nade! Get rid of that noob perk!"
"Whine some more, maybe they'll remove it in the next update. Fat chance, if you can't handle the heat, go play WoW nub."