Well, not exactly humor, but is it ok to have bits of it sound a little... casual, and chatty?
For example, One of the questions is the typical "why are you the best" and part of what I've written is:
Probably attributable to my frequent OCD tendencies, I despise leaving a job unfinished. Once I take on a task I commit to it fully, and a small, nagging part of my brain insists that I absolutely must finish it.
FYI, I'm applying to a coffee shop? Too chatty and un-serious?
OK, so what about
"Due to my specific attention to detail, I despise leaving a job unfinished. Once I take on a task I commit to it fully, and a small, nagging part of my brain insists that I absolutely must finish it. "