joker
noun [ C ] uk/ˈdʒəʊ.kər/ us/ˈdʒoʊ.kɚ/
(CARD)
（纸牌中可充作任何点数的）百搭牌
a special playing card that can be given any value and is used in some card games instead of any other card
(FUNNY PERSON)
爱开玩笑的人，逗趣的人
someone who likes telling funny stories or doing stupid things in order to make people laugh
He's always been a joker and can't resist playing tricks on people. 他总是喜欢开点儿玩笑，忍不住要戏弄别人。
(ANNOYING PERSON)
informal讨厌的人
a person who has done something that annoys you
Some joker keeps setting off the fire alarm. 一些讨厌的家伙不断触响火警。
Idiom
joker in the packidiom 能意想不到地改变形势的人（或事物）
the person or thing that could change the situation in an unexpected way