How it works currently: If you stand on top of a granade, and press the F-key, you should be able to throw back a granade. However, since even terrible fragger players cook their granades, the granades will explode before you are able to pick them up. (Not to mention that were you to encounter an uncooked granade, you just do not know the remaining timer on it. Therefore it would be stupid to rush to stand right on top of it.)
Therefore, the only way to make the augment really work as described would be to make it automated. Ergo, granades flying towards you would automatically bounce back. Yet it is not difficult to image how that could be considered over-powered.
Thus, what I would suggest is… What about granting the user an actual pineapple? Something akin to the delivarable objective container and turrets, ergo, you could bash the enemy and drop it down like the turrets are placed. In otherwords, the augment would largely remain as useless as it is, but offer a multitude of pineapple related humour.
(For example leaving one on top of an enemy player, or decorating the objective with one, or lining them up, or possibly just leaving one waiting to the middle of a room.)
And as far as I know, other games do not have Pineapples, so I guess there could be the meme potential.
Tired of teabagging your opponents? How about playing Dirty Bomb with us, we have pineapples!