I have a friend like that. Luckily the longer I knew her the less fake her smile was around me. Now I can read her mind even when we are miles apart, she now considers me a sibling of sorts and we have been best friends for over 10 yrs. Not all fake smiles are bad, a consider it more of a defense mechanism in her case.
I suppose, I just dislike them mainly because they always turn out to be evil and ride. I don't want to talk to someone who seems friendly but is actually insulting me in their head or thinks that they are superior to everyone else.
Your friend sounds nice though, probably just like how they say 'a friend to all is a friend to none.' It's good that you guys are friends, I pray that your friendship lasts very long.
I don't like people like him. The always smiling but totally fake.