I'm having significant trouble with this one for the following reasons:
The AT grenade does barely any damage
Vehicles are never present or near
Vehicles are forever loaded to the gills with the most switched on gunners in existence and/or there's the most switched on infantry nearby
Your kill is stolen before you get there (typical case where your team goes all out to destroy something you're about to, otherwise they don't)
Enemy tank is literally immune to damage. Strapped a piece of C5 to a tank that was on fire and successfully detonated it, only for it to not be destroyed
You cannot detonate the C5 after throwing it because it imposes a massive delay penalty that does not affect enemy players who toss three pieces and detonate within a second