Question for Ferox13 or other horror nuts

I remember when I was probably 12 years old (1980 - 30 years ago) my friend said he snuck into one of the midnight movies they had back then that showed that "graphic" horror stuff.

So I was never able to verify the movie, but the one thing he described I still remember to this day, and I have no idea what movie it was from, he said...

"a guy takes off his belt and then takes his belt buckle and starts to carve up this girl's stomach"

After all of these years, and seeing most of the cult horror films from that genre (Romero, Franco, D'Amato, etc) I have no idea what movie he was talking about.

I think the kid might have been feeding me a load of crap and the movie doesn't even exist, but I figure I would throw it out there to see if it rings a bell with anyone.

What you got OG horror experts?