At places like r/politics - you can get banned for pretty much anything. An example is that a redditor called me a Bernie bro and I sad "I pity you," and a mod permabanned me. But I think at most of reddit you can still use "Bless your heart."

One thing I do when I want to be 100% safe is say something like "You have given me much to think about​! You are wise, trenchant, and clever. Good luck in life," and then I disable comments. It's not nearly as fun as telling them "You are a fucking moron and I hope that [redacted]," but at least it's safe.