City of God is kinda violent.... real.... and a top movie too... Dead Mans Shoes is a great movie too, with violence... but neither of these are OTT... if it's OTT you want, with gore, then i don't think you can get more much violent than Hostel 1 or 2... or go on YouTube...
Johnnie Sunshine: Maximum Violence It's got person on person violence AND person on zombie violence (and vice-versa).
I know OP doesn't give a shit any more, but True Romance is a pretty violent movie. But, only the director's cut. The "pussed out for television" version is for Nickelodeon.