Well it's happening on Bungie's Instagram account, they're going around telling everyone horrible stuff. IIRC, Bungie has banned players from the game for real-life toxicity, harassment, and hate before

Unfortunately, they can only ban them if they know their Bungie Name IDs. Unless the user has posted their Bungie Name ID on their social media, there isn't anything Bungie can do on third-party sites.

I have their Bungie Name ID

Even if you or Bungie do have that information, they have to be sure they're the same person which isn't an easy task. This is why Bungie rarely takes action against people posting malicious comments on social media. The most they will do is block them on social media channels. The best option is to report them on the social media site, block them then move on with life. Don't waste your limited time with these horrible individuals because there everywhere. You will end up spending more time reporting than doing something better, like playing Destiny.

I mean, I understand the hesitation about being the same person and I'd considered that, but I do at least know for a fact it's them. If they were to say something in-game using text or voice chat, would Bungie be better able to take action?