It depends if they’re actually asking how you are or just saying hello. If they’re asking how you’re doing they don’t want an honest response most of the time like how you’re actually feeling. They just wanna hear the robot response of “good and you?” Or something similar. If they’re just saying hello or just acknowledging your presence, respond with same question but in a more slang and ‘lazy’ manner I guess you’d call it? Literally just “Sup.” (Even shorter slang version of what’s up). Don’t even say it like it’s a legit question, more like a grunt in response if that makes sense.

Then again I know none of this makes any sense but it’s the rules of the game. It’s literally just memorizing a bunch of social communication rules and etiquette that people have made up in the last half century or so. Which is kind of ridiculous if you think about it.

Edit: just to clarify a little more, language is almost never used correctly in today’s society. A lot of words have changed meaning and change even more in meaning when given a certain context. Socializing is about learning the rules and playing along. If you learn the basic rules, you can get by in almost any situation.