I usually start with
"hi sailor, new in town" (in a lispy voice)
that usually confuses them long enough for me to draw my weapon and shout (in my classic NY accent)
"freeze moxxxx fuxxxx or ill blow your Fuxxxxx head off!"
Its all in the tone of voice.
you can use the NY style warning for multiple situations
"back off MF'er or i'll rip your F'ing head off"
some folks like to add "and shxx down your neck" but i think thats a little over the top.
i offer online classes for anyone who wants to learn the NY style of threats