As gamers I'd like to think we don't look to offend others, especially our fellow gamers. At the same time, if you make your focus to never offend anyone at the gaming table, you are going to have a miserable time. You'll probably also fail miserably.
We all do it. Something said in jest that someone else feels offended by.
The secret as I see it, is not repeating the offense once it's brought to your attention. Which requires a gaming group that is open enough to discuss these issues briefly when they come up, and not let them fester.
I personally guarantee that I will offend folks, now and in the future. It's human nature. Just don't make it personal ;)