Wow. I've never thought about how I'd like to be talked to during a hard block. I'm one of a the few I guess who appreciate the sentence finishing. I read that most hate it, but I can't think of an experience where it bothered in me in the slightest. Sometimes I'm begging the person in my head to spit the word out for me. I think if there was anything that bothered me it's over smiling. Not like you're laughing, I can tell the effort is the smile to show acceptance, but it feels like pandering. Makes me feel like special needs person. Don't smile at a stutterer during a stutter unless the block is so funny that you can't help. Don't sympathy smile. Just give a normal, interested, conversational look and try to maintain eye contact.