BC: I've use words like cunt, fag (or gay), and retard for quite a long time as insults, which I know is terrible, especially because I don't use them to be derogatory toward women, gays, or the mentally disabled -- I don't know where this came from. I try to be very careful not to blurt out something Tourette style in mixed company... sometimes I think I might actually have a mild case (and I'm not joking about that).
The word-filter issue is kind of an interesting one. My ex has a 'slippy' filter, meaning that she normally switches between vulgar-among-friends and careful-elsewhere language modes . . . but sometimes she slips, as when she told my grandmother, many years ago, that she 'just really fucking hated' something.

Oops. But
c'est la vie, and my grandmother just pretended no slip had occurred.
As for the OK / not-OK word issue goes . . . I'll be honest: My feeling is that language IS about intent at least as much as it's about interpretation. And fuck all the rhetoricians, et al, who insist otherwise. As far as I'm concerned, it's not up to them, and if they get to tell me what it means when I say something, then I get to tell them what it means when they say something. I do not yield authority over my discourse to a self-appointed expert whose primary interest is what they think I mean.
Giving intentional offense is the speaker's choice. If you're trying to offend someone, and you do, well, right or wrong, you did what you set out to do. Unintentional offense is another story. If Bob is homophobic, and I call him a fag and mean it as a gay slur, and Bob gets offended, well, that's what I was aiming for. I used the right word. If Carl is listening and happens to be gay and takes offense, and I didn't intend that, well, then I screwed up. Although I may not care.
Just because someone is offended by something doesn't necessarily make it my responsibility. People offend me all the time. I often get mad at them, but I don't feel like they owe me something special. Members of oppressed groups have a better claim to deserving special treatment, but it's not an all-powerful claim. There's obviously a popular movement for groups to 'take possession of' slur terms and repurpose them (eg, 'That's OUR word!'), and I may be sympathetic, but that doesn't mean I agree that I don't have a right to use that word.
Anyway, I frankly reject the notion that when I typically describe something as 'gay' that it has anything whatsoever to do with homosexuality. I'm so-so with the alternative spelling 'ghey'. Meh. I also feel free to use 'retarded', although hopefully not around someone who will be unintentionally offended.
Still, you can't please everyone. A few years ago, I got in a LOT of trouble because I described a social group of liberal acquaintances as "touchy about politics". Some of the people I was talking to made unfounded assumptions about what that "touchy" was supposed to mean. In the long brouhaha that followed, I said more than once that I was sorry that people had gotten offended, but I refused to apologize for what I'd said or what I meant, and I still feel like I said what I meant and did nothing wrong.
I don't know if people are still mad at me over it, although I wouldn't be surprised, but fuck 'em.