The episode "Peeps" has Benson going over the top with watching Mordecai and Rigby through over a thousand cameras. It's serves as not only fuel for people with a voyeurism fetish, but also fuel for people who have a "Benson" fetish.
This same episode has a scene with Mordecai and Rigby walking in the same toilet stall. You could easily find a rational explanation, but maybe...
"Ello Guv'nor" features a Rigby terrified during most of the episode, in the cutest way you can ever think of. If you didn't hope Mordecai would give him a hug at some point in the episode, something is clearly wrong with you.
Also, Rigby going crazy on the taxi. Just wow.'
"Really Real Wrestling" Featured Mordecai and Rigby wearing little briefs the entire episode. For some reason this is kind of hot, despite them usually being completely naked all the time anyways.
In "Rigby's Body" there's a scene of Mordecai and Rigby stuffing themselves with food.
On that same train of thought, Benson eating pancakes in "Appreciation Day".
"Skunked" must have appealled to someone's skunk/flatulence/torture/transformation fetish.
It's pretty apparent that someone in the production team has a transformation fetish, as it's a theme visited in quite a few episodes: Mordecai and Rigby turning into Susans in "Benson be Gone," Doug turning into Rigby in "Temp Check," Rigby turning into a skunk in "Skunked," Rigby turning into a freaking house in "Terror Tales of the Park," complete with the other characters actually entering him--in addition to assorted zombification/ghostification/body switching episodes... There's probably more examples that this troper has overlooked, but there's more than enough evidence to confirm this.
Benson somehow manages to set off all of this tropers fetishes. Bondage, voyeurism, Hard-working, musician, ect...