(British, American & Australian) alsotake the biscuit (British & Australian)
if you say that something someone has said or done takes the cake, you mean that it was very bad, and even worse than things they have said or done before She's been opening my letters - that really takes the cake!
Be the most outstanding in some respect, either the best or the worst. For example, That advertising slogan really took the cake, or What a mess they made of the concert-that takes the cake! This expression alludes to a contest called a cakewalk, in which a cake is the prize. Its figurative use, for something either excellent or outrageously bad, dates from the 1880s.