[getone]

Um, this title is stupid. There's a difference between starting a comment with "I'm not a racist but..." and actually being a racist.

[rossriley]

From what I can gather that's the idea behind this project. It's one of those marker phrases that normally signifies offense is about to occur.

Eg. I don't mean to offend you but.... Don't take this personally but...

I'm not racist but.. is one of the most famous of these and often, though not always, signifies that something racist is about to be said.