Redditism 1: "It's the internet. You are allowed to swear." 
I hate when some very grown-ass adult says that because someone didn't cuss enough for their taste. I swear all the time in my posts here but I still find that shit really, really tryhard and it seems more immature than not saying the naughty word to me.
Redditism 2: Ending a rebuke with a question mark when it's not a question to make it sound extra snippy.
I've heard this being compared to a "vocal fry" and maybe it is, and coming from CA, vocal fries were often said out loud as a form of subtle hostility toward people perceived as lessers, such as retail and restaurant workers. If you need an example of what I'm talking about, it usually goes something like this:
Poster: "I think (opinion)." 
Redditism enjoyer: "You're wrong?" 
Redditism 3: "Do you need help? Who hurt you? Help is available if you need it, buddy!" 
This one is the worst one I can think of right now because it contaminates even the very possibility of showing sincere care and concern for someone else. It comes loaded with the implication that the person that was "hurt" or "needs help" is fundamentally wrong and should shut up. Fuck that ableist shit, forever. 
So, here, there's a constant jockeying for clout, you can watch a group of guys reinforce their social structure. An interaction might go like this:
Guy 1: I'm interested in topic X, it is new to me but I find it enriching and I hope you do too Guys 2-5: This is actually terrible, and you're an idiot for thinking this might be good and that we'd enjoy it. And this happens almost constantly regardless of whether the group actually goes with topic X as an activity.
It's an almost constant stream of belittlement and humiliation from all parties, regardless of whether there is any camaraderie or friendship. It is really exhausting, but I've noticed I've reflexively done it.
Thank you for the clear explanation, this is something I have observed too. Very antisocial culture especially amongst men.
I'm sure I could think of a specific example, but my brain is fried