- I doubt there is anything you can say to change your in-laws minds; I don't believe such opposition is rationally based, so I don't think you can rationally argue them out of it.
- I do think that regardless of their opinions, you deserve to be treated with respect. To me that means you don't need to be berated everytime (or every other time, or every third time) you meet up with them. They've made their positions clear, I believe you have made your position clear, and neither is likely to change. T'were it me, I would do some heavy consultation with the wife, and then make it clear, emphatically clear, to the in-laws that you are not going to tolerate being badgered, and if they can't let up, cut off further contact until they can behave. Pretty big threat, not one to bluff with, and maybe that is not possible in your situation. As I said, it is something I would do, don't know if you would. On the other hand, I do not see why you should play the nice guy and be on the defensive when your in-laws are spouting non-sense. They are not on the moral high ground here.
- I think Seamus came pretty close to the underlying problem -- "the reason is that having a weapon available is a reminder that bad things can happen." You may wish to reflect on Dave Grossman's parable about sheep, sheepdogs, and wolves. http://hobbes.ncsa.uiuc.edu/onsheepwolv ... pdogs.html You are a sheepdog, and you are making the sheep nervous because they don't want to believe there are wolves in the woods.
- Secondarily -- As a practical matter, it wouldn't have hurt your gun to get wet, as long as you cleaned it with in a reasonable period of time. HOWEVER, I like pranks as much as the next guy, but when someone says NO, I DON'T WANT TO (for example) BE THROWN IN THE WATER, proceeding with the action stops being a prank and becomes an assault. You don't need to articulate a reason they agree with, you simply should be able to say NO and end it. I hope at least your wife understands this now!
Good luck!
elb