For me it'd be dating columnists/"relationship experts". I genuinely cannot think of any more vacuous, timewasting or pointless profession.
For one thing everyone's an individual so all advice they give is basically essentially obsolete as soon as its read as no-one can guarantee what works for others will work in their own specific situation. For another thing it's an area where I genuinely am completely clueless as to how anyone becomes qualified as an expert. Anyone, and I literally mean anyone, who works as a dating columnist or relationships expert is simply wasting a space on the planet somebody else could be using to do something productive with their lives.
But enough of that. Who would you line-up against the wall?