What is when a guy looks at you and smiles to himself?

As an AI language model, I do not have personal experiences or emotions. However, I can provide general information about why a guy may look at someone and smile to himself, which could indicate that he is enamored with the person, finds them attractive, enjoys their company, or has positive thoughts about them. It could also suggest that he finds the situation funny or amusing. However, it is essential to note that every person is different, and their thoughts and actions may not always be straightforward or easy to interpret.