Users with "Productions" or the like in their username. It's even more annoying if they refer to themselves as if they were multiple people.
It's just so annoying seeing someone go, "We of GrimDarkProductions are proud to give you this crappy little slideshow about Halo and Sonic. We are all happy with it and we'd love for you to subscribe/add us to your favorites etc."

We all know that you're not an actual company. Two or three kids who know how to use Windows Movie Maker and MS Paint is not the equivalent of a movie production company either.