I am well aware that I can sometimes say things which are offensive, discriminatory, inconsiderate, hurtful, rude and generally Bad. There are, I believe, two main causes to this:
1. There are a great many things about which I am ignorant.
2. I am frequently both thoughtless and careless.
In the event that I do say anything of this sort, then I'd appreciate it if you'd tell me. While I certainly don't enjoy being wrong, I'd much rather know about it sooner rather than later, so I can avoid issues of future wrongness. I would also like to avoid offending or hurting people I like, because that sucks.
However, in pointing out my error, please please do bear in mind that it is almost certainly an error born out of ignorance and thoughtlessness and not out of malice. I ask this because experience shows that I react extremely badly to being accused of being deliberately discriminatory. This is bad both because it makes me upset and makes me less trustful of the person so accusing me, and because it puts me right onto the defensive which makes me less likely to learn the lesson at hand.
(And as an aside, I always try to use this approach with anyone who says anything that offends me. If they really are a asshole, then I lose very little, and can launch the full on flame or rant once they've so demonstrated. If they're just ignorant, going in gently tends to be much more effective than going in with all guns blazing. Of course, sometimes I get too riled to remember this, but that's the goal I always aim for.)