The stochastic highlighter — this is the habit of picking completely random bits of an article to highlight which drives me up the wall, usually a crime carried out by a well-known Medium bot who will remain nameless for the purposes of this article, though if you already know the name do mention it in the comments! Random highlighting has to be on the list, unless the highlighter is David Perlmutter, in which case it is a privilege to be highlighted extensively.