Clearing a hilly trail with ditch blades and machetes. I was about 15' - 20' ahead of another guy when I bent to tie my shoe, I hear this "wooosh" "ping" noise. The other guy had lost control, slipped, and thrown the machete and that was the noise, if I hadn't been tying my shoe, it would've caught me somewhere between the shoulder and mid head.
Once in the city, during a wind storm, I was about a building length ahead, when a bunch of construction material came off a high scaffold. That could've been nasty too.