1. When you haven’t read the post. This should seem obvious but really isn’t in practice. If you leave a fired up, hyper-critical comment on a post you clearly haven’t read, it’s embarrassing for everyone. This typically occurs when the commenter reads the title of the article, has an immediate emotional reaction, and then comments based on that reaction and not the body of the article itself. Someone blogs “How Shitty it Felt When I Came Out” and someone comments something scathing about how coming out should never be a shitty experience and how dare that person promote the societal expectation that coming out is bad when really the person who wrote the post probably said exactly those things.
2. When you have a personal vendetta against the writer, regardless of content. This usually occurs when a pretty, boring, stuck up, privileged girl you went to high school with starts a blog about her crafts/amateur photography business/pregnancy and a combination of jealousy and legitimate disgust cause you to leave inflammatory comments simply because you can. This can be even worse if this asshole is succeeding in a field you’re either in or feel incompetent of but wish you weren’t, like if they had an amazing graphic design blog or a successful Lookbook account.
3. When you’re jealous. This relates to but goes beyond the previous point. You might be jealous of a particular person’s lifestyle, but you might just be jealous of where a person has gotten published, whether you know them or not. If you’re a struggling, relatively unknown blogger, you might leave shitty comments on the Thought Catalog just because you wish it was you. If you feel jealous of an indie celebrity like Bebe Zeva you might leave some rambling, assholeish thing on a featured interview of her. Seriously, don’t do that. It just makes you seem pathetic.
4. When you hate the site. This one makes the least sense to me. I have seen it on both this and a dozen other blogs—someone comments something like “jesus the titles of your articles suck” or “you used to write X which was smart and Y is stupid” or something simply like “fuck this blog”. If you hate the shit out of a blog, stop reading it, right? Seems simple.
5. When you’re tempted to post anonymously. A good rule of thumb is unless you’re doing something like telling your secret internet blogger crush that you have a huge throbbing web boner for them, if you’re thinking about posting something anonymously, you’re probably being an asshole. Take out the swear words, dial down the reactionary impulse drama, and maybe just go make a cup of coffee or something.