One sunny afternoon, I was walking down a relatively large downtown street in Canada, when I head a loud voice from across the street:
Nice shirt! Looking good!
I immediately turned my head and spotted a middle-aged man. He was looking at me and doing a thumbs up. I smiled and continued walking.
How should I have responded?
There was nothing special about my t-shirt. It was just a plain orange t-shirt.
If the compliment seems positive and sincere and you want to acknowledge it politely, a smile and a wave or thumbs up is appropriate. You can say "Thanks" or give a compliment in return if the situation allows for it, but if shouted at for a distance you aren't required to shout back.
If you're talking about an inappropriate "compliment" or remark being shouted at you, what works best for me is to ignore and not even acknowledge that I heard it, since any response, positive or negative, will tend to escalate the situation.
This is just my experience from getting some friendly random compliments and some uncomfortable unsolicited comments on my appearance while commuting by public transit and working in the city (in the Northeast US).
