When someone posts a full thread, because even 500 chars (or more, depending on the config of your instance) aren't enough to explain a full argument, you should take the time to read the full thread before commenting. Especially when your spontaneous reaction is a sarcastic/snark/codenscending thought. Be respectful. Deal?
@jwildeboer I get that on Twitter a lot. My favorite phrase is, "I'd love to have an intelligent conversation about this, but it sounds like you didn't read my arguments."