Right when I got to high school, around '77/78 or so. It was an 8mm tape of the "phone repair guy" showing up at a house to repair the phone- duh, only to pork the lady of the house and her friend. Two older, hairy bushed, skanky old ladies.

I remember thinking WTF is the big deal. Didn't watch any more until years later, it had Ginger Lynn in it and my opinion of porn shot way up.