An enormous being the size of a subway train, created to build the giant cities of the Old Ones. Just seeing it is a mind-blowing thing. The name means "Inhabitant of the kingdom of darkness."
Currentaly living in vast lightless caverns and tunnnels under Antartica.
It was a terrible, indescribable thing vaster than any subway train - a shapeless congeries of protoplasmic bubbles, faintly self-luminous, and with myriads of temporary eyes forming and un-forming as pustules of greenish light all over the tunnel-filling front that bore down upon us, crushing the frantic penguins and slithering over the glistening floor that it and its kind had swept so evilly free of all litter... "At The Mountains of Madness" by H. P. Lovecraft
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!"