Or enjoying a sunny day across the ramp, roughly a mile away, and all of the sudden a KC-135 tanker blows up. That's a bad day too. Amazingly only one person died, but that sticks in my head vividly. Very rare event. It was undergoing maintenance on the line and a short or something from a wingtip light lit fuel vapors from a vent in the wing. Very rare and odd as the flash point of Jet A is higher than regular aviation gas. The ground shook and the magnesium in the brakes made it look like the 4th of July.
Been in the situation of a head on collision. I was safety pilot for a guy practicing approaches and a guy came out of the sun head on, I screamed pull right full power, and may have shit my pants. We were making all the calls, but this guy was just out burning holes in the sky, and obviously not monitoring any frequencies.