Lizard crosses it with his invasion of the trailer. He rapes Brenda, kills one of the birds, shoots Lynne and Ethel, and considers shooting Catherine. Easy to say he's probably the most despicable character in the movie by that point.
Big Brain ordering Lizard to kill Catherine just to spite Doug for killing Pluto.
Ruby, the mutant who protects Doug and Catherine from her mutated family.
Venus and Mercury, the two mutant children. The fact that they don't attack Doug and act like normal kids (in contrast to their family) is a bonus.
As noted by his actor, Michael Bailey Smith, Pluto almost qualifies, with his simplistic, childlike mindset. Unlike Lizard, hurting Catherine doesn't appear to cross his mind, though raping Brenda certainly does.