be (as) rare as a four-leaf clover

To be very rare or uncommon. A clover with four leaves instead of the usual three is traditionally thought to be a good-luck charm due to its rarity. Please, who would I even ask to the prom? A high school boy who isn't a doofus is as rare as a four-leaf clover. Passionate love like you find in a poem has always been rare as a four-leaf clover in my experience. Support for the president is as rare as a four-leaf clover in this part of the country.