(noun) This condition usually occurs after you've played a console game too long. But was prominent with the original Nintendo Entertainment System
back in 1985 with the original box controller. After many long hours of gameplay be it Zelda
or whatever game you were playing, you would begin to feel pain in your thumbs and it would work its way up throughout your hand. But you usually wouldn't stop playing because you wanted to beat the game. But this condition can still occur with just about any game console controller
Sam: Yo man I'm going to beat this PS3 game.
Tony: Ok I'll go watch a movie.
*three or four hours pass by Tony walks back into the room seeing Sam still at it.*
Tony: So how much further do you have to go in the game?
Sam: I'm almost finished but I'm developing a bad case of Nintendoitis
A condition very common among 8-bit games, but can be applied to any game in which this happens, even if it's not a Nintendo game. It is a condition in which an enemy that was just killed would respawn in the same place if the screen scrolled to the left and then back to the right (or right then left). This condition is most prominent in games like Super Mario Bros. 2
Hey, I just killed that guy! He came back while I was going for that 1up! This game has Nintendoitis bad.