Super Mario Bros. I knew all the tricks. Minus World, Little Mario that shoots out fireballs etc. Of course the infinite lives trick and all the warp locations.

Porn games such as schoolmate and homemate. Girls be so horny for me

Tough question, it's been a while since then...

I guess it could be TMNT, both on the NES and the Gameboy (why everyone fears the Dam Level so much on the NES is something I'll never understand) or Golden Axe Warrior on the Master System. On PC, either Dune or Fantasy General.

Super Smash Bros. Brawl

I used to beat Punch Out, Double Dragon II, and Shadow of the Ninja pretty much daily, sometimes several times a day. I would often play with the controller behind my back for a little extra challenge.

Looking back, it's pretty amazing how little content most games used to have. They were also incredibly expensive so I would end up playing the few games I owned over and over.

Donkey Kong Country 3. I know every single inch of this game.

Not sure I have one. There have been some I have been very good at, but as time goes by without playing them continuously I tend to loose it. Also, when I get really good at a game I find playing it somehow turns into more of doing best instead of enjoying myself, so I then move onto something I find FUN again.
Maybe bubble bobble, or Snow Bros, I played the hell out of both of those but it's so hard to compare to many other players and they were just fun as hell.

Hm, Mario Kart 7? Maybe Pokémon X/Y and Roller Coaster Tycoon 3 (the best one)

And I bet you enjoyed every minute of it. Now that you have more money and likely lots of games, how many have you played through more than once, or even once? I can say the same. I haven't played through quite a few games I own now... In some instances they almost seem too long lol. At times I just need a break.

Probably pac man, only had that and ski on my computer so I played them a lot.