I know for a fact that Rarity wasn't banned for the theymos thread. Not going to tell you why Rarity was banned because I'm not sure I can disclose it, or else I would tell you.
I was under the impression he was banned for the thread about dank he posted in Scam Accusations.
Rarity and Dank have been going at it for ages. If Rarity was officially banned for that it just seems like an excuse. Besides, if anyone was trolling there it was the guy who intentionally played a poor version of Mary Had A Little Lamb just to get a rise out of her.