The combed giraffe sings like a saucepan
I came across a number of interesting French idioms today in this article in The Guardian, including peigner la giraffe (combing the giraffe), which means to waste time on a pointless task, and chanter comme une casserole (to sing like a saucepan) or to sing terribly. It also mentions a Dutch idiom, broodje aap verhaal (monkey sandwich story), which refers to persistent rumours or urban legends.
English equivalents of peigner la giraffe include idling, dossing (about), doing nothing (much), killing time, and so on. Do you have any others?
How about English or other language equivalents of chanter comme une casserole or broodje aap verhaal?