Desmond has a pure hatred for poop and pregnancy testers. He seems to be a caring person who wants the "demon poop" to stay away from the children. Even though he's a janitor, he seems to really dislike the poop and having to clean up after it. Desmond also seems to be friendly and likes cleanliness as opposed to dirtiness.
Voice actor Aaron Krebs came up with the idea of a Jamaican janitor during the recording of the first season, as seen in the Season One two-part special, "The Making of The Most Popular Girls In School." Despite loving the idea, the creators were unable to fit the character into the plans for the remainder of the season, leaving the character to be the first character to appear in Season Two overall, as well as the first addition to the show in the second season.