I'm going to tell my friend with Asperger's that his word shouldn't be taken at face value.
Why would you do that? Can you tell me why you would doubt your friend?
He is being so annoying with his words that I doubt everything he says.
If a friend has been causing you to doubt what he says, then you should talk to your friend about what is going on. It's important to be considerate and understanding with people who have mental disabilities such as Asperger's as they cannot control their condition. Saying that you doubt everything your friend says isn't going to change his behavior and will only cause him to feel hurt.
I'm never wrong.
It is expected that people respect one another, including people with disabilities.