I'm an American, I've lived several major cities (so I'm not blinded by a specific localized culture), and calling people "guy" as a generic pronoun doesn't strike me as a universal Americanism. Where it is used, it's just as a greeting:

"Hey, guy..." or "Hey, dude..." or "Hey, man...". I prefer just "Hey" or "Hi" to get someone's attention. "Mister" and "ol(d|') guy" seem anacronistic to me. (I was born after Vietnam if that helps.) "Mate", "chap", etc. are the same idea, but originate in British (or colonial British) culture.

Those attention-getting pronouns are frowned upon in formal or "civilized" (upper-class or upper-middle-class) communication, I suppose because it's considered informal or rude to try to grab someone's attention that way. However, in everyday vulgar (as in not-formal) speech, I don't consider any of them to be insulting. There are other culture-specific race-specific and gender-specific pronouns which can be very insulting, to the point of getting you killed when used in the wrong situation, but can also be okay depending on who you are and who you're talking to.

When talking to cops, border guards, or any agent of the executive branch who has the power to ruin your day, I would always use "sir" or "ma'am".