You are an Alien Overlord, and one of the planets in your domain is rebelling or otherwise misbehaving. What would be your extermination method of choice?

Spectacle.

The idea isn’t so much to destroy the insubordinate planet, but to send a message to the others that insubordination will not be tolerated.

The exact method is a hairy question. It must be visually compelling (the destruction will of course be televized on all propaganda machines on all subordinate planets) but not give the impression that I’m doing this for emotional reasons or that it is anything more difficult or important than swatting a mosquito.

The Genesis Device would do well, I think, if I had it. Instant removal of all annoying life forms, and leaves behind a nice, freshly terraformed planet. Perhaps for use as a penal colony?

I’d force the rebels to join and participate in Fluther. It’s slow, but it would kill most of them in time

I think I would be a benevolent overlord. If this planet didn’t want to follow my rules they would be allowed to opt out of my empire. But they would lose everything I had to give them. It’s all or nothing.

Efficiency. Ice comet impacts. When the planet’s orbital lanes clears of ejecta enough for re-colonization I will give it to a people who knows how to behave for colonization

Isolation and silence… the silent treatment. Or I would make it a dry planet, no smoking or drinking, and no pot.