Strangers following me? All too easy.
Loud shouty voice, strong hand on weapon, weak hand outstretched:
"What the F- do you want!?
Why are you following me?
Are you F-ing crazy?
Get the hell away from me!!!"
Of course if they turn out to be Mormons or Jehovah's witness they learn a lesson too.
Sorry for the cursing but that is what I would say....
Oh and never walk straight to your car if people are following you.