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Johnny's typical catchphrase is "I ain't sayin' nothin'!". Johnny is in his 30s. He is one of the mobsters working for Fat Tony, besides Legs and Louie. Johnny has short wavy black hair, thick eyebrows, and wears a pinstripe shirt tucked in a purple suit.
Like his nickname, Johnny says very little, which spares him from accusations of being a "squealer", but his reticence tends to be unhelpful to himself and others. An example of this is when there was a shoot-out in Fat Tony's mansion, and Johnny was shot by accident. When asked where he was injured, he replied, " I ain't sayin' nothin'!", and when asked what to tell the doctor, he said, "Tell 'em to suck a lemon." 
Fat Tony has referred to him as his "Joisey (Jersey) muscle." 
Despite his occupation as a mobster, he also seems to have an altruistic side, as Homer has once revealed that Johnny digs wells in Darfur on his vacations.
Behind the Laughter
Johnny Tightlips is a reference to Frank "Tight Lips" Gusenberg, who was shot down in the real-life St. Valentine's Day Massacre in Chicago and replied "nobody shot me" while dying.
On the "Insane Clown Poppy" commentary, it is discussed that the original name for the character would be "Tightlips Johnny"