It's the same for me. Even when I curse I don't stutter unless I'm trying to demonstrate that. Personally I think I don't stutter when I'm angry because I'm not thinking about it. I'm not thinking about what I'm saying or how I'm saying it, I'm not worried about my stutter. I'm distracted with my anger, tired of whatever crap I'm dealing with and I'm just trying to get my point across. I don't know about others, but my speech is better when I'm distracted doing something while I talk. Usually.