I can only imagine the kind of pressure a comedian faces with having to be funny 24/7. But, at the same time, I do expect professional jokesters to be humorous at least half the time when doing something publicly. Of course, that's more so a fan's rule—and one which a number of comics don't abide by on social media. Maybe they have their reasons. Say, not giving away material they can sell or just not essentially doing free labor in 140 characters. Whatever the reason, though, there are way too many comedians who aren't funny on Twitter. Here are the 20 biggest offenders.