standing joke
noun [ C usually singular ] uk/ˌstæn.dɪŋ ˈdʒəʊk/ us/ˌstæn.dɪŋ ˈdʒoʊk/
长期的笑柄;（尤指恶意的）经常拿来取笑的事
something that a particular group of people are familiar with and laugh about often, especially in an unkind way
The fact that Debbie is always late has become a standing joke among her friends. 黛比老是迟到的事已沦为朋友间的一个笑柄。