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.)
In my experience, 帥哥 is more addressed to refer to young people. It's like "Hey young man" in English. No matter what, being young is a beauty. People call the young generation 帥哥 in memory of their own long passed golden youth years.
帥哥 is just a noun commonly use in Taiwan and sometimes in China. It have the same meaning to "sir"(not Madam!!), but more causal way to greet someone. You can also use it to a stranger as more polite and respect. Normally you won't use the 帥哥 to a friend or family.
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.
Meaning: handsome guy.
Frequency: females use this word, males seldom use it.
A literally handsome guy;
Greeting, commonly used in market;
Humour, to exaggerate the ugliness of a guy.