Acronym for "Sorry honey, it's Thursday." Used when someone says "TGIF" a day early.
A blonde gets into an elevator and sighs "TGIF!"
The brunette already in the elevator shakes her head and says "SHIT".
The blonde says, slowly and carefully, "T.G.I.F."
The brunette insistently says "S.H.I.T."
The blonde says "TGIF stands for 'Thank goodness it's Friday, you idiot!"
The brunette responds "I know. SHIT stands for 'sorry honey, it's Thursday'."