The most common uses of these sentences happen (mostly to me) while laying in bed at night.
"Oh, that one boy, Shiggity Sean, what a dreamy man. I can't wait to stare at him later... Oh, Shiggity Sean!!!"- Mom walks into bedroom asking if you are okay, you say yes, she leaves, and you keep fantasizing about the almighty Shiggity Sean.
What you may say when you really want to swear because you're excited or otherwise, but the congregation, support group or other prude association that you're affiliated with may be offended if you outright swear.
"Fack-Shiggity-Shak" I just won the lottery!
"Just stubbed my big toe, Fack-Shiggity-Shak that hurt!"
A news cast that was hosted mainly by a Shauna AKA The Queen Of The Interwebs from The Best Damn Tech Show.
Though as of November 16, 2007, Shauna left and now Scriggity has dwindled down to nothing.
soo...as of right now it has no current definition, Thus making it a fun word to scream out causing mass confusion...It means whatever you want it to mean.