What's the most alarming experience you've had with a stranger?

I was once stopped at a red light waiting to turn right. I glanced left, saw it clear, and started moving forward…but a tattered, sunburnt dude in a wheelchair had appeared out of nowhere and tried to cross in front of me.

I stopped in time, didn’t hit him, but must’ve scared him (or something), ‘cause he lost his fucking mind and started shrieking bloody murder, backed up a bit and started CLAWING at the passenger side window — not trying to open the door, just clawing, freaking my friend the fuck out — and screamed (exact quote), “I’LL KILL YOU, YOU MISERABLE BASTARD!!!”