A person, explanation, or occurrence deemed to be untrustworthy, fallacious, faulty, and generally just plain sheisty and/or disagreeable.

Also taken to mean gross/grimy + faulty.
"Hassan was trying to copy me during the test, but he couldn't read my handwriting and wrote down a bunch of wrong answers. What a dumbass."
"Shit is SO gralty, nigga."
by SillySausage69 February 3, 2009
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