It worked with Mike Tyson in "The Hangover. " But can director Todd Phillips make a celebrity cameo uncomfortably funny with a much more, er, complicated figure? The New York Post reported this morning that Mel Gibson will play a Bangkok tattoo artist in "The Hangover 2. " Two people close to the production confirmed to The Times that Gibson -- who's maintained radio silence since recordings apparently capturing his violent rants against ex-girlfriend Oksana Grigorieva surfaced this summer -- will play an American expat living in Thailand. (The gang goes to Southeast Asia in the new installment for the wedding of. . .