... yep. Another "My Dog Was Attacked By Another Dog Who Really Shouldn't Have Been In A Position To Do It" thread.
Out this morning. My dog offlead, sniffing happily in the long grass. People pass by with 3 dogs - a couple of Westies (I think) and a Collie-type. Collie is walking quite nicely, offlead, next to woman.
They pass by where my dog is sniffing and footling about in the grass. She takes no notice. She then comes out of the long grass, towards me. At this point, the offlead, at-heel Collie notices her and turns back, away from its owner, to approach my dog. Owner starts shouting the dogs name and yelling things like "Don't you dare!!" which leads me to believe it's already known to be a bit unfriendly.
Anyway, it ignores her and carries on approaching my dog who has now noticed its approach and has turned to it, ready to greet. She is just standing there and it launches itself at her, grabbing her neck and she ends up on the floor, squealing.
So I run over growling and yelling and it lets go.
Owners do come over, going "Sorry! Oh, he's a Very Bad Dog!!" 
YOU CLEARLY KNEW IT HAD ISSUES SO KEEP IT ON A FUCKING LEAD!