A grenade, often in FPS games, that does not go where intended that may:

1) Bounce back and harm and/or kill you.

2) Miss the target completely.

In the Counter-Strike Source Mod known as Zombie Mod, an improperly thrown grenade (or any grenade thrown by a n00b) results in failnade, which instead of hurting the zombies, propels them forward into whatever spot you are trying to defend, resulting in failure.