I have a stutter which comes and goes; it's been quite bad for a month now. My friends are awesome about it: they wait quite patiently for me to get done, and they don't make a big deal about it. In fact, once a week or so, they'll actually crack a joke or two about it, which kinda normalizes it. I know that might seem odd, but it helps me feel more normal, though I warn them if they begin to go overboard (they're 18, like me, I don't really blame them if they forget and cross that boundary). 2-3 weeks back we had a really important presentation (timed as well), so for that my friend asked me if he could interrupt me and complete a word/sentence, which I allowed him to do, but otherwise they know its more helpful for me to just get over the block myself, and not make the situation weird. One thing you might want to do which my friends do is toss your friend into the deep end: if you go out to a restaurant/café, make your friend interact with the waiter. It's really helped me gain self confidence when I need to talk to strangers with my friends there as support. There have been moments when I've embarassed myself in front of them, but they're decent enough that they haven't mentioned it or made a big deal of it. If you need any other help in interacting with your friend, PM me :)