How to choose between “of” and “for”

Question

This question is about the times when you want to use two different nouns to describe the same thing. Some examples, all of which may be used in a sentence of the form "He has X":

• a broomstick for a curtain pole
• toast for breakfast
• this pisstake of a salary
• some skank of a mistress

In each case, I believe I have chosen the right preposition, but feel free to correct me. I am trying to see if there's any kind of rule to determine if the preposition in between should be "for" or "of". Is there any rhyme or reason?

Answer 1

An X for a Y = an X as, or in place of, a Y. The broomstick was being used instead of a proper curtain pole.

An X of a Y = a Y which can be described as X.