Should I be concerned about pretend gun play?

If there's no way he can get his hands on a real gun, I'd say to just ignore his nonsense.

Do not give it any attention whatsoever. Do not react to it in any way. If you react he will do it more.

Just ignore him and he'll get tired of doing it if it gets him no attention.

My mother always did this exact thing, using her hand as a "gun" and I found it more irritating than her usual shenanigans which were irritating enough, thank you. 🙄 As her dementia progressed, she was fond of "play shooting" more and more people and political figures she disliked, mostly because she knew it annoyed me. I just ignored her nonsense and suggest you do the same. Gotta pick the battles you choose to engage in with the demented elders lest every doggone thing become a battle.

I agree that unless this is common behavior from the past or he has a history of some sort of mental illness/sociopathy then I would think it's part of dementia and that *maybe* family should be concerned about it.

My SFIL had Parkinsons and Lewy Body dementia. He regularly threatened to kill us so we made sure to remove his rifle that we knew he owned.

What does FIL's wife think about this? Is she a vulnerable adult (someone with cognitive or physical impairment)? Is anyone the PoA for FIL? If he has dementia then no amount of 'splaining is going to change this behavior, but rather redirect the conversation or distract him. If this behavior increases or escalates, please consider it threatening and call 911 to report it. It may be a situation where he needs to have a "social admit" for psychiatric problems. What's to prevent him from picking up a knife as a weapon? Your family will need to seriously think about what to do with this situation if the wife is at all vulnerable.

My father with Alzheimer's does something similar, he was never an angry or violent man but now likes to pretend to use his cane as a weapon. I always discourage it and tell him he can get himself in a lot of trouble if he does this in public. Have you tried asking your FIL why he does it? Maybe remind him that it is not funny and it hurts her feelings and makes her sad. I wouldn't worry too much about it as long as he has no access to a real gun and doesn't exhibit any other signs of violence.

Caregiver, this disturbs me, I'm sure it also does you.

Yes there could be dementia, but with that I'm also wondering if there is some built up resentments in your dad towards your mom that are boiling up and coming out because of dementia.

I would be concerned with other things he could say or even do. I feel like your fil needs to go to doctors, and your husbands family should keep a close eye on things

This is his dementia.
I would be very certain that no one laughs about this behavior, but shuns it.
And as mentioned below, given his current ideations, I would insure there are no guns in the home.
I would encourage placement in facility as soon as possible so that this woman can have some quality in her life ongoing.

You are sure there are no guns in the house?
Does he still drive?
Is there any way possible that he could get his hands on a gun?
Has he made any other threats or has there been any other indication of violence?
If not I would just keep telling him that it is inappropriate to do that.
There can be personality changes with dementia.
If there has been no other indications of violence I would not overly worry but if it escalates let his doctor know.