I'm not going to tell you some of them because it's utterly mortifying. I'm one of those awful people who's not very good and thinking before I speak. Don't worry, I'm working on it! I don't tend to get embarrassed by much but this does get to me. These things slip out, it's like I can see the words flowing out of my mouth. I can hear the joke forming in my head and it's almost like a compulsion to speak it. Afterwards I usually feel awful, mean, embarrassed, thoughtless and all other adjectives you can think of.
Now of course people have a right to make any jokes just like we all have a right to be utterly horrified by some of them (see rape jokes). I'm not saying I'm not allowed to make jokes just that I really need to do my best to think & hold back at certain times. I do always follow it up with apologising profusely afterwards. I would save myself and the other person much embarrassment and hurt by just not doing it in the first place.
On the flip side though some of my terrible jokes have been successful, very successful even. Maybehaps I need to work on gauging situations and people as much as thinking before I speak.
What about you? What bad trait are you most mortified about?