I ran into a DM who led me on and left me hanging. Made me write a background, a character sheet, everything, then got someone else to fill the role I applied for. DM stopped talking to me, didn't even tell me he didn't want me anymore.

I've run into people like this on other sites. My solution is to block them so I don't make the mistake of joining their games in the future. It's not worth the wasted effort and drama and permabans - one nasty incident on another forum had multiple people coming to my defense and to the DM's defense getting banned. Neither of us, the two main people in the dispute, got banned, but I left that site because I didn't like being around there anymore.

There doesn't seem to be a way to hide another person's games here on rpol.net. I can block rMail but this doesn't seem appropriate since none of us have sent rMail to each other, and neither of us have been anything but civil.

Is there a way to do this? Or should I just write down the person's username so I can avoid them in the future?

The only real way that I'm aware of is to simply remember their screen name and to avoid those games. There isn't a method to black certain games from being found on the searches or seen in the Player's Wanted Forum.