Oh heavens, I know the feeling! One day, in Petsmart, I was in line with Jake. A lady gets in line behind us with two pugs screaming bloody murder at my Jake! He thought they wanted to play. Thank goodness they did. They were very friendly. If I would have had Layla with me and they did that to her, God help those pugs.
Another time, I had Layla with me and an old lady (older than me) had a poodle and it was barking it's head off and growling at Layla. Surprisingly, Layla was calm but then the lady heads towards us saying "look, he 's not afraid of your big dog" I took off with my 'big dog' and never told her my Layla has a slight dog aggression problem and she could easily rip your dogs head off!
I do know if one of my big dogs acted like that people would freak wondering why I brought such a vicious dog into the store. My Jake is little but doesn't act like that or he would be trained not to or wouldn't go to the stores! In all fairness, I have seen plenty of small dogs that were very well behaved.