Learn English – What’s a better word for “cowardly”, that doesn’t sound like name-calling

When you don't know how to use your firearm, you become a menace.

As used here, menace is a noun meaning:

A person or thing that is likely to cause harm; a threat or danger

Have you considered using the Dreyfus model of skill acquisition? In particular, his ranking is:

1. Novice
2. Advanced beginner
3. Competent
4. Proficient
5. Expert

Note that each level has a specific, quotable, empirically-driven definition that allows one to (more-or-less) unambiguously identify which category one belongs to.

That might be helpful if your application is a self-survey which is otherwise vulnerable to differences of interpretation: a standard model has the benefit of normalization (to a larger extent than, say, “on a scale of one to ten. . . .”).

That said, since perfect standardization is an impossible ideal, if you implement this, you might consider offering an "other" option.

Alternatively, the word specialist comes to mind.