Social disorders; guns....
By social disorders I mean someone who has a serious documented problem where they may harm themselves or others. It would also mean they can't work or be employed due to unstable behavior or actions(suicide attempts, involentary commitment, threats, etc).
If you have ED or you stutter(speech empediment) you're not actively trying to kill other people or take hostages or are held in a psych ward.
There are SERIOUS levels of mental health or social disorders which should keep someone from owning guns or ammunition.
You're not "crazy" or unstable "sometimes", you have have a medical condition that requires medication and/or treatment.