Reserved for the harmlessly stupid and truly meaningless, vacuous is a smart-sounding way to describe something dumb. Celebrity gossip and reality TV are usually pretty vacuous, even if they're fun.
If someone smiles at you in a way that seems fake or empty, you could describe the smile as vacuous. An example of a vacuous comment would be a politician promising to make things better without explaining how. If something is vacuous, it's like a vacuum — hollow, empty, devoid of substance.