I was going to say we don't really have easy access to weapons here.. .but then I saw your pic, (you really do have a pic for every occasion!) and thought yea well we DO have knives...sooo with that in mind my answer is....
I don't think i have ever had to threaten anyone with a weapon... but I have given more than a few very withering looks and a severe telling off from me is probably just as deadly :P