How do you know whether someone is being 'irresponsible' before they catch the virus? Do you follow them around, taking photographs? Imagine the social stigma, for starters. Do you live in the real world, or a computer game?

You could go to karaoke bars, or other danger areas and hand out vaccination vouchers.

Or you could go by demographics. The hardest hit groups in the worst spreading areas. Etc.

You're right that it's not a trivial thing, but if you wanted to do it, reasonable approximations could be found.

It's not realy moral hazard, it's about what is the goal.

If the goal is to slow down the pandemic, then the "irresponsible spreaders" should be vaccinated first.

On the other side, if the goal is to punish "irresponsible spreaders", then they should be vaccinated last. But that also means that pandemics would not be slowed down, and the ones taking that decision will be responsible for further spreading.