I've also noticed that you can throw them underwater sometimes. However that doesn't always work.

Maybe designed on purpose... it's possible to thorw grenades IRL and can lead to some interesting tactics to 'nade a rooftop while on the ladder

It good to throw nades off ladders, but even better would be to see an an animation

Yes, I would add the animation, but it would be difficult as it would have to track eye position to see if you want to throw the grenade up or down and execute the appropriate animation. Actually, that doesn't sound that difficult.