carl
n. countablen. a slang name for a person who is very boring or follows the rules too much. It is often used to tease someone who does not want to have fun or take risks.
n. a pejorative slang term for a person perceived as dull, socially awkward, or overly conventional. Used primarily in informal British and Australian English to mock someone for a lack of personality or excitement.
Don't be such a Carl; come out to the party with us.
He refused to go on the roller coaster, so his friends started calling him a Carl for the rest of the trip.
From Germanic, cognate with English Charles. * From German and other north European Carl and Karl. * From Latin Carolus.
Shortening.
Used as a common noun rather than a proper name in this slang context; often follows 'be such a'.