I've said it before and I'll say it again - it's impolite to interrupt and speak over other people. Even if some people who stutter are ok with it - it's rude if you don't already know it's acceptable. As a stutterer who's had someone "speak for me" - it's humiliating. It feels like being treated like an upset child that can't speak and needs to be 'babied'. I've excused excused acquaintance 'A' for speaking for me when acquaintance 'B' told 'A' not to speak for me - because I just didn't want to be the center of attention - because I can't speak. Even if a stutterer say's it ok - it really might not be.