How to get myself banned from purchasing a gun.

This will likely not be successful in NH because NH doesn’t regularly report to NICS.

Maybe the OP could insist that he reported to NICS.

What if OP goes to a neighboring state and gets diagnosed as a threat to self/others there? NH isn’t very big, so this wouldn’t be a lengthy road trip.

I’m guessing that a simple visit to a physician would do it; OP would just need to declare his concerns, i.e. “I’m concerned that if I have easy access to a firearm I might buy one and kill myself someday.” Can we get a physician to chime in here and declare whether this would be adequate grounds for declaring the OP a threat to self/others, such that he could be banned from purchasing for five years?

No one is permitted to purchase firearms in a state which they are not residents. So theoretically the OP could move to a different state and never get an updated ID. Without in state ID or a way to prove residency an FFL will not complete the sale.

Probably best to just close this at this point. Those who wish to start a more general discussion may open a new thread.

The OP’s question specifically asked for ways to get info into the national database that could prevent him from purchasing a gun. Your commentary did not come off well, from my perspective, and was borderline jerkish in the context, but I will take you at your word for now that your intent was to be helpful.

This is not appropriate in IMHO; please don’t name-call.