The original one said something like "Thanksgiving isn't racist, change my mind," which is like... Not a thing that anybody says. The way Thanksgiving is taught to American kids is racist and full of revisionist history, but not even the ideal reddit caricature of an SJW would go around telling everyone that eating a turkey and mashed potatoes makes you racist. It was like inviting people to dEbAtE him on an issue that people aren't really even trying to make, so he'd get to sit there like a smug asshole without having to do anything.

Edit: I remembered the wrong slogan, the original sign said something else. The Thanksgiving bit was from a video he did, iirc the title used the same "change my mind" naming convention.