Tough guy was a slang nickname for a man who would bully weaker people.
In 2364, while encountering Data, Lieutenant Dan Bell was told by a vendor that he was from South America, and Bell said to Data, "Wherever you're from, while you're in my town, keep your nose clean. Well, tough guy, this time you've really done it. Your goose is cooked but good." (TNG: "The Big Goodbye")