Bad Kitty

Disclosure: I do not consider cats to be bad luck. I have six cats and one of them is black.
I do like cats with attitude, however, and these cats can certainly claim that honor.

Mahakala Misfortune Cat at MintyFresh

Grumpy Bad Luck Cat T-shirt at Domestic Platypus

13 Black Cats T-Shirt from Threadless

3-Eyed Cat Patch from Nice2MeetYou

Unlucky Cat Print by MagenMitchell at Deviant Art

Misfortune Cat by Playge