Can I just tell someone with ADHD to shut up?
Why would you talk to them like that?
I sick of listening to his rambling
I can see how this person would get on your nerves but it's good to try to have some compassion for their plight. Maybe tell them how their behavior affects you.
What do you mean? I'm only telling him to shut up.
Well, just telling them to shut up is rude and will likely offend them when you didn't have to.  Letting them know how their behavior is affecting you though can help them to be more accommodating without any hard feelings.