I feel this so much. Sometimes, I want people to finish my sentence to end my misery when trying to finish a sentence. Other times, I enjoy the satisfaction of finally completing the sentence. I think it also depends on how they're finishing the sentence. If they're doing it in an annoyed manner, it's awful. The number of times I've had people look at me angrily and say, “Slow down,” sternly is beyond me. It's awful.