OK since we're the ones who AREN'T the rabid child-eating nightmare dog owners - let's list the ones you've seen that just make the mind boggle. I'll start with a couple of mine that I've seen.
"Trevooooooorrrrr come back 'ere or I'm gonna kill you" as a means of recall! (No way I'd have wanted to come back to that horrible screechy noise - even if I didn't understand the kill you bit)
The woman who showed up to my dog training class - no treats, nothing... not even a dog-lead, but had the dog restrained with a plastic swing bin liner tied to his collar (and did so fairly regularly by all accounts).
Dog owners who drive to the park, don't bother with those lead things and just open the car boot, letting the dog run straight across the carpark at will. This one's a regular pet-hate of mine.
The guy who felt really really aggrieved (and swore so much they turned the air blue) when they got bollocked by the dog wardens for not owning a collar (see the previous section on just opening the car boot and letting the dog fly out).
The bin-liner one just blew my mind though.