The vacuous expression had dropped from his face like a mask.

There was a vacuous, doltish expression on his face.

So, he smiled broadly, but not with the vacuous expression of the holo-Dominic beside him.

She had a bland and vacuous expression.

It bounced toward its victim, its expression vacuous and innocent.

John Marshall returned in a few minutes wearing an indescribably vacuous expression.

He was about sixty, with short gray hair, a pleasant square face but a vacuous expression.

You can tell by his vacuous expression.

The vacuous expression was frozen solid as Gillbret lay there on his side.

This was not the vacuous facial expression of a woman whose main purpose was to provide distracting eye-candy for the customers.