Noun - The occurrence when you have stayed up late enough at night that you not only forget what day it is, but also think that what you did mere hours ago actually happened the day before.
Tom: "Hey, Katie said you messaged her three times tonight, I think you shouldtake the hint, dude."
Bill: "Oh, crap. I forgot I already had! Bad case of dayfusion, man."
Tom: "Maybe you shouldn't stay up so late?"
(Plural: darfi) An American student traveling to Europe for a school trip, usually in a large group. Possesses no concept of how not to be a dumb tourist, will probably have their wallet stolen and lose their passport.