“I’ll bet this guy is a real douche bag.”
Might be libelous.
Could be. I would say that it was my bet, not something that is a definitive statement. I can have an opinion. I suspect someone stated some facts that weren’t true and that got them in serious trouble. I would at least hope it reached some bar equal to slander or whatever. If someone’s thoughts are fair game, everyone is in serious trouble, and I’m not just referring to the internet.