Chad Kroeger RIPS Avril Lavigne's Ex-Hubby -- You're a NOBODY!!!

Avril Lavigne's ex-husband ... JUST GOT OWNED BY THE GUY FROM NICKELBACK!!! Here's what happened -- Deryck Whibley and his hot GF Ari Cooper went to a Halloween party this weekend dressed up as Avril and her new fiance Chad Kroeger. Deryck was Avril…

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