Not X
Let X be one of the following: homophobic, racist, sexist, transphobic, or xenophobic (or any other of a seemingly ever-expanding set of bigotries). I submit for consideration the following hypothesis:
Someone who is actually not X will never have to say, "I am not X".
Introducing a statement with "I am not X" means that the speaker knows damn well they are about to say something intentionally X. They (sort of) know it's wrong, or at least not completely socially acceptable. They are just determined to say it anyway. They hope the X statement will somehow redeem their prejudice, even though all it ever manages is display, never redemption. Anyway, they don't really care all that much if it redeems them; there's a catharsis they seek in saying X things.
It doesn't get any more X than that.
By the way, these are the people you hear complaining about having to be "politically correct". These are the people you hear complaining that they don't enjoy "freedom of speech". They don't realize that "freedom of speech" only means the government can't pass laws against saying X things. It doesn't mean everyone else in society has to slurp up every X thing they say with a spoon. It doesn't mean there are no consequences to saying X things.
I believe these people seek to return to a society where all the X opinions were the dominant opinions. One almost had to say them to mark oneself as one of the privileged. We'd like to think that if such a society ever existed, it's at least half a century in the rear-view mirror. But the fact is, there are people now trying to establish or re-establish it in 2015. Some of those people are unaccountably credible candidates for President of the United States.
Now it's certainly not the case that only X people ever say something X. But if someone who is actually not X ever happens to make such a statement, they soon recognize their error. They apologize for it, and they seek to learn what they need to learn so as not to repeat it.
As it turns out, that entire process also never requires them to say, "I am not X".
h/t Clare Cosgrove