A Dog's Breakfast(2007)

Man's best friend makes the worst accomplice.

If you've never been good at anything in your life, why would murder be any different? Patrick has always had a somewhat combative relationship with his little sister Marilyn, but when she brings home her new sci-fi soap star fiancé Ryan, it's all out war. When Patrick fails to drive a wedge between the happy couple, he reaches for sharper instruments.