What is Teaching A Pig To Sing?
1.
A quote from Robert Heinlein: Never try to teach a pig to sing; it wastes your time and it annoys the pig.
Usually applied to someone that has a character flaw or annoying habit they will never change because they simply aren't able to.
A person with bad hygiene - you tell them they stink but they don't really care.
"Getting you to clean your room is like teaching a pig to sing; it's a waste of my time and all it does is annoy you."
See