Do you see someone making a logical fallacy on Reddit? Or are you just looking to learn more about logical fallacies?
This website contains a list of logical fallacies (with an explanation and example) and serves as data host and front-end companion for Reddit bot.
Right now, the bot is in testing stage. You can test it out at /r/fallacybottest by making a comment "keyword + fallacy name", eg "fallacy in appeal to probability".