Armchair experts. People who make up fabrications on the spot over a subject they clearly know little to nothing about, yet cannot handle being accused of lying.
People who seemingly can't think for themselves. A common example being that if you were to post a comment that features a term or counterargument that a replier isn't familiar with, instead of looking it up themselves or paying attention to the context, they instead are all like 'wHaT???' or 'aNd...?.' Likewise, if the person's counterargument is too vague or is simply nonsensical, refusing to explain themselves also makes them just as bad.