Joker (comic strip)
WordNet
noun
(1) A playing card that is usually printed with a picture of a jester
(2) An inconspicuous clause in a document or bill that affects its meaning in a way that is not immediately apparent
"When I demanded my money he showed me the joker in the contract"
(3) A person who enjoys telling or playing jokes
(4) A person who does something thoughtless or annoying
"Some joker is blocking the driveway"