"Euthanasia" just means "good death". And in common usage it means killing something not as punishment or to serve your own interests in some way but for the "greater good"; so executions aren't euthanasia, slaughtering animals to process their bodies or as by-kill in pursuit of some other aim is not euthanasia, and killing for sport or amusement is not euthanasia. Basically, it's killing with regret and respect for the being killed and without selfish intent.

So "euthanasia" doesn't mean what you suggest it means.

Gaining consent is voluntary euthanasia. You can have non-voluntary euthanasia. However, you are correct that this isn’t euthanasia but for a different reason - you euthanise something to put it out of unbearable suffering.

This is extermination, not euthanasia.

It's pretty common to refer to destroying an aggressive dog, for example, as euthanasia. This is an analogous situation, particularly given that, as pointed out elsewhere, honeybees are domesticated animals. I think this could fall under euthanasia for behavioral problems.

I think that's a mistake in terminology. The dog is not suffering, others are suffering. Normally when I hear reports of dogs being killed due to aggression, the word I hear is "killed" or "destroyed".

I think it does actually matter. Killing because of aggressive behaviour is execution, not euthanasia.