Intended to be in the same vain as "That's What She Said", used when someone inadvertently makes a comment that could be interpereted as sexual in nature. The result of which makes it seem as though the speaker embarks on this kind of thing weekly. It originated from the movie "The Usual Suspects" where 5 characters are jailed, and one states after being strip-searched...
Fenster: Man, I had a finger up my asshole tonight.
Hockney: Is it Friday already?
"Man, you sprayed that shit all over me!"
"Hm, is it Friday already?"
(While playing Halo)
"Damn, man. I got shot by 3 guys at one time."
"Oh, is it Friday already?"