Ask questions, meet dancers, and be part of the conversation.
I don't look at it in a negative way. I look at the change in attitude as a milestone. People who did not like me the first time are now eager to dance with me. I have improved myself so that I can dance at their level. Each milestone opens me up to a greater range of potential partners. It would be petty of me to look at it as vengence as everyone just wants to have an enjoyable time.
If you want to add a little ribbing, you can do so in a joking manner. (e.g. "Remember when I first dance with you..."?) Then the two of you can have a hearty laugh about it.
As for the OP, I don't hold it against guys who wouldn't dance with me when I started out, because honestly, I don't remember! The only ones that I really hold a grudge against aren't the ones who've turned me down, but are the ones that have been rude to me when we danced. There are guys still today that either won't dance with me, or will only dance with me under certain circumstances...I don't hold it against them, I just either don't ask them and wait for them to ask me when they're in the mood, or only ask them at the times I know they're likely to accept - and enjoy dancing with them when they do, and take their accepting/asking me more as a sign of improvement on my part.
As far as the later conversation goes, I don't hold anything against the above guys, because I can be just like them, although for probably different reasons. I admittedly can be a dance snob, but it usually is more connected to my own dancing than theirs. If I'm having a good night dancing, I'll dance with just about anyone. If I'm having an off night though (or an off MONTH...), and I'm having trouble dancing with guys that I almost always dance well with...I'm not going to want to take my chances with someone I don't know, or someone I know to have issues that negatively affect my dance (for example, the guy that I have to work to stay on balance with on a good night, I'm not going to want to dance with when I'm falling out of balance on simple turns with good leaders). When I'm having an off night, the only people I really want to dance with are my friends and the ones that I know won't throw me off.
As far as guys that I generally don't dance with, it's not the beginners I have a problem with - I'll even often seek them out...it's the "experienced" ones that have been dancing for years, aren't good leaders, and never improve (and usually think they're hot s**t too!) - and have copped an attitude with me at some point.