It’s not your data.

Fuck off.

Sort of, but not really. From the Reddit ToS:

By submitting Your Content to the Services, you represent and warrant that you have all rights, power, and authority necessary to grant the rights to Your Content contained within these Terms. Because you alone are responsible for Your Content, you may expose yourself to liability if you post or share Content without all necessary rights.

You retain any ownership rights you have in Your Content, but you grant Reddit the following license to use that Content:

When Your Content is created with or submitted to the Services, you grant us a worldwide, royalty-free, perpetual, irrevocable, non-exclusive, transferable, and sublicensable license to use, copy, modify, adapt, prepare derivative works of, distribute, store, perform, and display Your Content and any name, username, voice, or likeness provided in connection with Your Content in all media formats and channels now known or later developed anywhere in the world. This license includes the right for us to make Your Content available for syndication, broadcast, distribution, or publication by other companies, organizations, or individuals who partner with Reddit. You also agree that we may remove metadata associated with Your Content, and you irrevocably waive any claims and assertions of moral rights or attribution with respect to Your Content.

It’s actually a fascinating bind Steve/Reddit has put themselves in. Because it is a non-exclusive license, you can affirmatively declare your content is free for anyone to scrape or use.

After that, if Reddit ever asserts rights over your content by, say, suing Microsoft for improperly using your content in training data, you now have a legal claim against Reddit for interference with either your ownership rights or with a contract via whatever license you have made your content available under.

Now, maybe Reddit has a claim release in their TOS, but it wouldn’t prevent you from getting an injunction enjoining Reddit from restricting your data from being used by Microsoft.

It’s kind of academic, because… it’s not really a victory that Microsoft is also training its AI on your data. But, hey, they’re probably doing it anyway and at least this way we get to screw over Huffman for being an ass.