Two weeks ago, heavily pregnant suffering from bad SPD so with a crutch, I was out walking with 2 year old DS on public (owned by a local nature trust) fields. Everyone is welcome there, dog owner or walker.
A golden retriever, head to toe in mud, headed towards us at top speed and only swerved at the last minute. Naturally I adopted a defensive stance and said "shoo" because, hey, I didn't want to fall over nor did I want my poor toddler flattened. I was not showing signs of fear, I was just bracing myself.
Apparently the dog was "friendly" and I was "over-reacting". I said I couldn't be too careful, as I'd seen one loose dog kill another on a lead in a park before (true - it was horrific) which is my stock response to the "friendly" excuse these days. The dog continued to circle and wouldn't return to the owner despite him calling, albeit extremely pathetically.. we couldn't get past. I told the man to keep better control of his dog.
His response? To tell me that I shouldn't be out and about if I couldn't control my legs(!) and I was irresponsible to have DS with me 
There were a lot of things I wanted to say but given I had DS with me I had to settle for "You're not a very nice person at all, are you?" as he finally disappeared into the distance, yelling things I couldn't make out, and still not having his dog under control.
Totally ruined what was supposed to be a final mummy and DS special time together before the baby arrived 36 hours later. I don't "do" confrontations very well at the best of times, let alone at that time.
I used to be a dog owner too, so I'm not entirely unsympathetic. However people with badly trained dogs and with an arrogant attitude ruin it for all the ones who do things properly.