Yeah, I called 999 once when I witnessed a car crash.
I was walking home from a night out on the town, very drunk, stoned and tripping, and came to a roundabout at the end of 3 long roads.
As I crossed the roundabout and road I suddenly heard this roaring engine, a squeal of breaks, then a bump as a car flew over the roundabout in front of me and crashed into a lamppost on the other side of the road.
Two people clambered out of the battered wreck as it started to burn, and ran off, leaving me stunned and amazed at what I had just witnessed (it's not every day you see a flying car).
I ran across to the nearest phone box and called 999, in a very excitable manner "Oh my fucking God! A car just flew over my head and exploded! It's on fire and you've got to send a fire engine quick! It's so fucking cool!".
The police and fire engine turned up, and quickly got the blaze under control and questioned me about what I saw exactly.
The funny thing was, because I was still very drunk and high, excitable but also very nervous because of The Guilt (that horrible feeling you get when on illegal drugs in the presence of police), it took a lot of repeated effort to give a calm and collected account to the police, without waving my arms about, making explosion noises and saying "fucking" a lot.
To their credit, the police were patient with me, and even though they could see I was high as a kite, they took their time to listen to my account and didn't dismiss it as the exaggerated ravings of a drug fuelled loser. I'm sure they realised that as excited as I was, that was understandable considering what I'd witnessed, and all the evidence confirmed my wild story - very short, intense skid marks before the roundabout indicated that the car must have been travelling close to 100mph, didn't see the roundabout until it was too late, launched over it like a ramp (indeed flying through the air as I said) and hit the lamppost on the opposite side of the road.
We even had a good old laugh afterwards, sharing a cigarette and shooting the breeze, as when they were inspecting the obviously stolen car, they found the front littered with leaflets which exploded out of the dashboard... the leaflets were all 'Crimestoppers - Lock Up You Car and How To Prevent Vehicle Theft' guides, not that they did the owner much good in his car.
Until the day I die, the night where I was almost decapitated by a flying car, and saw it's bright lights pass in front of my eyes whilst tripping, will remain one of the coolest things I've ever witnessed.