I do hear people say that a lot to me in China and I am always surprised by the timings and situations in which people just, kind of bluntly I feel, say this. I wonder what all those situations would be where someone could say that to you and why it's been said so often, it seems prioritized to saying some other, more proper things (I believe) sometimes (as if appearance is the most important thing "to talk about and mention", giving it a lot of priority.)
帥哥 (shuai ge), though it literally means "handsome", has nothing to do with one's appearance. It's just a polite way for addressing a young person.
Any situation, in English, where one might say "guy" or "gal" can be replaced by this. So, anytime you may want to draw someone's attention or someone else may want to draw your attention, you could just use 帥哥.