Mike you little liar

I guess Pixar wanted the money so badly they just had to ignore Mike

Maybe it was just an exaggeration?

I've always wondered about this lol. Maybe they were friends before but they got out of touch lol idk

The director said it's an expression that they use in the monster world

Actually, the director of monsters university wanted to play that line out by having sully and mike meet in the fourth and having a time jump to their college years. However, john lasseter and monsters inc original director told him that it'd be best to omit that idea for the sake of a good story. And like mamani14 said previously, the line is viewed as an old monster saying.