I've not actually called 999 (In UK) but I've caused it to be phoned twice (I'm not a criminal)
The first time was when I was walking home from College and some drunk idiots thought it'd be funny to throw a Tea mug at me, which smashed at my feet, and then follow me, corner me and then headbutt me because I "Broke their cup"
The Gene pool is so high round here honestly, they probably would of done more, but they underestimated the nerdy boys speed. (Thank you Football ability, and your preference towards left wing

haha)
They never got caught obviously, there was CCTV but it was focused on the road instead of the pavement, so all you saw were about 4 shadows chasing another shadow

Still, I got £2000 compensation out of it, some of that went on my Skyrim preorder actually

Anyway!
The second time was when I looked out my window (which looks out onto a little woodland pathway, it's not really "woodland", it's like a little stream side path in between houses) and someone had set fire to a motorbike and we were worried it might have fuel in it still.
Also, just on a random note, that wood pathway is also frequented by sixually promiscuous teenagers who like to engage in "illicit" acts.
I'm not sure what's worse though, that they do it.
Or I immediately start laughing and update my facebook status.
Sorry for tl;dr people