I've been undercover playing with Tonton, he seems to be a fair player. If he killed you with that nade he might have done it for fun purposes, I also do that sometimes
You cannot report a player if he teamkilled you ONCE. If you have reports with multiple teamkills, not by a grenade then thats a different story. Many players teamkilled me on purpose once and he didn't say sorry and I left him playing, but if he insisted of course I banned him.