I can't think of a phrase using milk that means last straw, height, epitome, or brim.
I wanted to add that the vulgarity associated with milk and cream, as Poli mentioned, is not widespread. We say (and buy) milk and cream all the time without thinking about the possibility that it may be taken the wrong way (that it may seem vulgar to some). There are many words that have both a good and a vulgar meaning.
|