"Fire in a crowded theater" comes to mind. In reality, the judge making that comparison later rescinded it, and the guy won his case (about distributing anti-war pamphlets) anyways.

Ostriches sticking their heads in the ground.

Living fossils.

That prokaryotes are "primitive" life.

Eskimo words for snow.

"Anal" behavior.

Essentially all popular metaphors are based on misconceptions, really.

Basically everything from this list https://en.wikipedia.org/wiki/List_of_common_misconceptions