"Smile guy" is used to describe a person that walks into an already started conversation between a group of people and then just stands and smiles. Usually, the person is not really great friends with anyone in the group, and after not talking for a while, begins to feel awkward. After hes not acknowledged for a while... he just walks away. Db.
Look at Schersh standing in that group lookin like a doofus! He must be a smile guy.