The scene where the meme originated.
It's over 9000! is a popular internet meme originating from the popular anime "Dragon Ball Z".
Development
In the original Japanese version, Vegeta's line was "It's over 8000!". This was changed in the dub to match Vegeta's lip movement during this bit of dialogue.
Fan Use
TeamFourStar did a video on YouTube, as part of their abriged series of Dragonball Z, satirizing this error. In the dialogue between the two, Vegeta responds with "It's over 8000!", Nappa then says, "Aw, Vegeta, you didn't do it right!" Vegeta responds with "Yes I did!"
Use in Popular Culture
In the visual novel game "Phoenix Wright: Ace Attorney", the character Sal Manella uses the phrase.