Had the same thing happen to me many moons ago..
I was looking for the MOH:AA install disc and knew my cousin had a bunch of CD's in his PSU box, it was a big fancy one with a carry handle stuffed full of manuals and random accessories. I was digging through and pushed aside a couple of driver discs, I then found a set of discs in a spindle at the bottom. At first I found a burned disc titled "XXX", I knew I was on shaky ground but assumed it was just a bit of family fun with Vin Diesel. However, the next disc confirmed my suspicions. "Midget Gang Bang".
I called him MGB for months, he had no clue. When I finally told him why I had been calling him MGB, he just said "Oh yeah, I need to give that back".