1. Couples.....you never know what their comfort level is, especially the woman's, But I will approach if they show interest in me, but that's one of the few times I wait for a customer to make the first move. I've had great customers who were couples and made a lot of money off them, but I've also encountered some mean, nasty, insulting, change throwing female customers. They seem to usually be one extreme or the other....great or just horrible, so that's why I usually wait for them to make the first move whether it means wave me over or tip me.
2. I haven't encountered many gay guy customers. I can count them on one hand, and yes they DID enjoy the stage show and weren't really into lap dances which is okay. They were great tippers.
3. I love fat guys in the clubs. I will usually approach them first. 9/10 they spend pretty good money.
With that being said, the tone of your post was pretty condescending so you can't be surprised by not so friendly responses. It's okay to wonder why dancers don't often approach certain kinds of customers and okay to ask, but you would have gotten more pleasant responses if you had asked in a nicer way. When it comes down to it, we're independent contractors (mostly) and free to approach or not approach whoever we want to. If someone doesn't want to approach a type of customer that you normally like approaching and do well off of, why worry about it? That's more money in your pocket.