So I'm out on a trail run today.  DFW trails suck, but beggars can't be choosers.
Anyways, lots of people with their dogs on these trails.  I love seeing dogs out there.  The vast majority of dogs are well-behaved.
This one group, with a German Shepherd (or Belgian Malinois, can never the difference), is walking toward me (as I run toward them) along the trail, and this short woman, maybe-120lbs-soaking-wet, sees me coming and immediately strengthens her grip on the dog's leash.  Digs her feet in as well.  She gets low for leverage, really girding herself for a struggle.
The trail is tight, but as I approach, the dog just goes ape####.  Growling, snarling, teeth, barking, etc.  Full aggression.  Chickie is really fighting to hold the dog in place.
I go way wide on the trail (off-trail and into the brush, actually), and it's one of the few times I've been legit afraid of a dog when running.  I'm shocked the chick could hold the dog back.  If she couldn't, I'm pretty sure I'd have some very serious injuries right now.
So, just after I pass, I turn back and yell to her "you really shouldn't have a dog like that on the trail".  She totally ignores me and keeps walking.  No apologies or anything.
What if I had approached the group from behind and she wasn't ready?  ####.