I'm not ashamed to say that he would have had barely a glance, if I'd even noticed him, a palm right in his face, and a loud, very clear 'No to whatever it is.'
In my younger days, although I was clueless at the time, I was seriously stunning (I have seen the pictures), and was constantly fighting off attention from men who thought their time was more important than mine, headphones and frankly hostile stare from me notwithstanding. I learned very quickly that 'What book are you reading?' was the precursor to a pick up line, and that a swift ' Sorry, mate, not interested' was nearly always followed by 'Don't need to be such a bitch, love'.
Now that I am a grumpy old woman, I care not a whit, and if I respond at all, it's just ' go away.'
So, no,OP, you don't have to talk to, be polite to, or smile at anyone you don't want to unless they are your boss ( and you need your job) or someone who is threatening your child. Screw all these men who think they are owed something, simply for existing.
And for all those who will come back with, well, not all men are like that - how are we meant to tell the difference? Do they come with signs we can read before they call us bitches?