Choose the word which is different from the rest.

The answer is D. Paragon.

A ruffian is a violent or disorderly person. A criminal is a person who has committed a crime. A gangster is a member of a gang, especially a criminal gang. A pirate is a person who robs ships at sea. A paragon is a person or thing regarded as a perfect example of a particular quality or type.

Paragon is the only word in the list that does not refer to someone who is considered to be bad or criminal.