By what you described, it would definitely be a mutual kill situation, and for the sake of it not turning into a "well fine, I'll just shoot you next time", both players should take it. Obviously, there are a lot of younger players still learning the game, so take that into consideration when this sort of thing happens. That being said, work on saying it. Most of us that have played for years are bad about it (I am fighting the old "Hey you!" all the time), and of late we have all been putting a focus on actually verbalizing the "Safety!" or "You're Dead!". It takes some getting used to, but if you do they can't argue it quite like that.