An even coarser variation of the already popular troubled youth phrase "Shut up!"
"Excuse me, sir, but I missed the trolley. Could you be so kind as to take me to the town square in your horseless carriage?" "Shaddup!"
by Chris December 22, 2003
Slang form of "shut up," (shut your pie/beef hole, plug it, quit yer damn jabbering, etc.) for those who haven't the time to articulate the entire phrase.

Also similar is Shutcherface.
"Shaddup down there, can't ya see I'm try'n'a sleep?"
by kraftdinnerclone May 22, 2004
An Australian slang term, used to express a strong fondness for someone's body. Typically used when oogling.
*Female Japanese tourist wanders into a redneck Australian bar*
Jap. Female: Ah! Konichiwa!

Aus. Male: Oh, shaddup shaddup!
by South East Queenslander March 30, 2018