Taking Coals to Newcastle

Back in college, one of my friends was dating the daughter of a florist, and he told me that he never knew what to get her for Valentine's Day, because bringing flowers to a florist's daughter was like taking coals to Newcastle.  I told him that those two things were nothing alike, since flowers are pretty and smell good, and coals not so much.  Also, his girlfriend was nothing at all like Newcastle.  Some men aren't very good at relationships.