Sounds like K cough @tizwozliz
@LadyCatStark I view dog etiquette as not letting your dog approach another dog unless the manner of approach is reciprocal.
So on lead: if they move towards one another and the owner doesn't stop it...rock on.
Off lead I still think there is still etiquette but under doggie control and this is the bit dogs need help to learn. So if a dog is indicating playful behaviour...rock on. But if like my terrier they are ignoring your dog which then continues to chase her or get into her space you need to call your dog away. This is the really hard behaviour to train and I think a longline is essential unless their recall is solid.
My terrier is scared of big dogs and will happily run off lead, playing on her own. If a dog approaches she will ignore, divert direction and generally avoid. If they don't leave her alone I recall but big dog is then chasing her and she gets more scared. She eventually turns around and has a snap at them. The vast majority of owners understand this is OK as without their dog bothering her nothing would happen. It worries me however because one day a big dog might then retaliate and my 6kg terrier could be mauled.
So recall is your answer. As long as you can recall your dog if they are bothering another let them off lead.
The bit about learning this is done on lead on sight of other dogs. So their initial reaction is to turn to you rather than overflow with "ooooh dog lets play" excitement
Last night on the beach a big dog headed aggressively straight at us. (My two off lead but mooching close to me) I immediately scoop littleun up as I know she will launch into defend panic and the other dog would probably kill her. Big un I'm just keeping hold of so I can manage the situation. The other dog recalled immediately.