It's the same as saying I don't feel like going,except you put "Tomorrow" in for a Buffer. :)
Because, in that instance, we're already sure we won't want to go tomorrow, because we don't want to go at all.
I've either got the blahs or something better to do.
It's a more polite way of saying "I absolutely don't want to go to your awful event and probably won't call tomorrow, but I'll leave the response open-ended to give you hope."
It's a nice way of saying, "Kiss off."
Pretty much everyday's the same anymore so I already know
Because you can make an informed guess ba<x>sed on how you feel now + what will happen between now and then