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1.
scottish slang to describe the unfortunate one with an under-bite.
"sham gabbit"=someone who,s lower jaw protrudes further than their top jaw therefore producing an over-bite... flip side being "gabbit sham" =an over bite, where the upper jaw protrudes over the lower jaw..

"his sham gabbit was so blatent! and he had described himself as handsome!!! apparently not so!! "
by wicked -ice May 11, 2010