Usually said in a really bad italian accent, is used to discribe the state of ones mind after a massive drug binge especially after back to back nights of no sleep.
"Hey mate how you feeling after last night????"
"EHHH, i am scattar!!!"
To eject fecal matter with such speed and ferocity that it rebounds on whatever surface you are aiming at and hits you in the behind, quite like a boomerang.
I just had the worst scattarang ever. It bounced right off of Phil and I got bruises all over my frikken balls.
Dude, don't eat at that shitty place, you'll scattarang for sure.