I was playing before ratings and I probably bought Turrok first but the first one I bought that I remember being Mature was Konker's Bad Fur Day.

If I'm not wrong. In my family, it was we got GTA III on our family PS2. It was wild to witness that kind of game for the first time. Honestly, looking at my siblings playing with the cheat codes they found was a marvelous experience

Mortal Kombat 3 for SNES

P0rno tetris in ~2000, I think it was on a completely legal CD with 300 games most of which were bite sized platformers and fighting games but also some jewels like Carmageddon.

Considering I am pre-raitings, it would probably be Mortal Kombat 2 for the SNES. It was also the first game I ever pre-ordered. Man, was I excited to get that game.