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. 
Beginning a post with "Eh," means I can safely disregard whatever contrarian take to follow
I do that all the time at work when I hear a lib take.
"Kkkamala is gonna tax unrealized gains!!"
"Eh, she's not gonna do it while also having a lower capital gains tax than Reagan, as well as wanting to build trump's wall, she really is pushing the same policies trump was in 2016, they said he was a threat to democracy but she isn't somehow?"
Then they start asking why I'm defending trump..
I'm fairly certain most people I work with think I'm a Trumper without me ever having mentioned him or ever saying anything about him in particular