When a friend does something you really dislike, don’t give them the silent treatment. Not only does it fail to help them improve, it also creates an atmosphere where they can’t ever be sure whether or not you’re angry at them, and they can never be truly comfortable around you. 

Tell them what the issue is, not just so that they can take it as an opportunity to improve, but so that they can be at ease around you. If they know you’re going to be honest to them when they mess up, they can feel comfortable knowing they’re doing the right thing when you’re silent.