This happens to me a lot where people go for handshakes and "bro" fists and I have no reason to reciprocate, I barely know the person or I just don't like them.

The problem is they just stand there, waiting, eventually asking something like " u gonna dab me up bro?, just gonna leave me hangin man?"

For people I don't like Ill respond to these with either no to the first response or yes to the second, and maybe walk away. But I haven't figured out how to respond to people I hardly know. I don't really want to disrespect them and not reciprocate, but it all seems so immature to be bumping fists, or shaking hands with some guy I barely know given the context.

Keep in mind this isn't any sort of business situation, for example the other day I got into a short group conversation with some friends, and a younger guy at the gym(18 or so) joined in. The next day Im there and scenario 1 happened exactly, he just comes out of nowhere right up to me during a rest time and says "whats uuuuup, ya lil manlet" (this was in reference to the conversation) and holds out his hand. I look at it, and back at him then he says "u gonna dab me up bro?" I said to him "no, and Im not a manlet" (I'm 6'6 btw) and went back to working out.

I feel like this came off too defensive, and ultimately wondering how I should handle situations like this in the future.