man, what a horrible feeling that we can't even go pick something up without some idiot hassling us these days... I can only imagine how scared you must have felt, especially given your prior experience 10 yrs ago...
I work for a large restaurant franchise here in CA. We have homeless, drunks and aggressive Aholes sometimes hang out in front of our restaurants begging for money from guests... the minute we know about it they are told to leave immediately. If they refuse, they are watched closely while we wait for the police to arrive. In the future, absolutely go back inside the store and ask for the manager. I guarantee they are not thrilled to have someone outside scaring away their customers!
You have no obligation to be nice to someone who is making you feel threatened. Even if you don't perceive it as violent or if they don't mean to be threatening... it's OK and the right thing to do to simply say, "Please leave me alone." If they do not it's time for action. I am nice once, and if they don't get the clue the nice act is over...
I hope you are able to move past this and forward again... hugs...
There is a fine line between "hobby" and "mental illness".