Oksana -- Mel Gibson Is a Liar!

7/23/2010 4:01 PM PDT BY TMZ STAFF
Short, sweet, and to the point -- Oksana Grigorieva flat out called Mel Gibson a liar this morning.

Oksana -- who denies her sister was the one who leaked the infamous tapes -- isn't nearly as long-winded as Mel is.