I think this would bother me, too. I just saw something similar to this on Dirty Jobs today: Mike Rowe was working with this guy who, while they were talking, started a sentence and trailed off without finishing it; this bugged Mike, so he started finishing the guy's sentences for him. I found it funny, but also true for me. It's not that it makes me mad, but I feel kind of anxious if someone doesn't complete a spoken thought. (OCD.)