While I agree with you on StoneDross being God-awful and obnoxious, I'm not sure I can call it the worst there is in good conscience. Without the author's grating political preaching and desperate attempts to get social media attention, the comic's art is merely functional and bland without ever being overtly offensive to look at it. When a strip isn't about politics, it rises to the dizzying heights of mediocre.
As for comics that are still active, I was tempted to nominate Sonichu but that at least has a funny-bad charm to it sometimes. I checked and discovered that "Least I Could Do" is still being made, so I'm going to go with that. It's a sick power fantasy for the author and it makes my skin crawl in ways that even this StoneToss prick can't manage.