Is an unpleasant smile the same as an unhappy smile? What does an unhappy smile look like? If they're not the same then what does an unpleasant smile look like?
"Unhappy smile" is a smile that makes the person look sad.
"Unpleasant smile" is a smile that is meant to make other people feel uncomfortable.
"unpleasant smiles" are used when the person is angry or upset, while "unhappy smiles" is involuntary, and is a result of being sad, or unhappy personally.