I personally don't think the comments are that bad. If someone can't handle being told to slow down and concentrate, then that person's got other problems to worry about I reckon.
Calling a streamer (or anyone else, for that matter) a "kid with bipolar disorders" is not just telling someone to slow down and concentrate, in my book. Plus, Piranjade didn't even mention the reaction of the streamer themselves; they might have just dismissed the messages, for all we know. Maybe the streamer *did* handle being told to slow down and concentrate. I wouldn't blame them if they didn't handle being told they are kids with a bipolar disorder, however. Or that this is a "thinking man's game", which implies the streamer is dumb and not a proper "thinking person", thus making the game one of those elitist titles that just some "enlightened few" can truly appreciate and enjoy. All of this is kind of rude and offensive, to me, honestly.
I don't know if that account is Cleve's, or not, but either way they behaved like a self-entitled elitist douche and, yes, they were downright offensive, those messages aren't just trying to convey "cool down and focus", they are telling someone that they are childish, have mental disabilities and are not "worthy" of this "superior" game.
[EDIT] Ninja'd by Piranjade. I figured the streamer would have been mostly cool about the messages.
Well he didnt call the streamer a kid with bipolar disorders, he said the game wasn't for kids with bipolar disorders. Even if he did call him that, its not a big deal.
I think people are far too easily offended these days, and that's coming from an SJW like me.
As others have said above, there are plenty of other more valid reasons to not like Cleve.