I submit that for a strict definition of "Unsympathetic", it is unlikely that anyone in the comic has felt sympathy for Jimbo. Awe, disgust, head-shaking astonishment, the desire for an air freshener, but not sympathy.
But for a more straightforward explanation, I just don't think Jeph likes writing arseholes. A totally unsympathetic character is a two-dimensional one, as I'm sure we all agree, and he likes to flesh them out a bit. The closest he's come to a genuinely bad person in QC was the VespaVenger, and even she had a Freudian excuse and a website full of fans.
Also, with regards to Dale: I've said in other threads that if you try to slant your perspective just a little, what he's doing is actually as creepy as all hell with serious stalker and implied-threat undertones. Pretty much everyone in-universe takes him with good humour, and when he's not trying to intimidate Marigold he's a regular guy, but I'd like to see more of him as a person rather than a rejected Saturday Morning Cartoon villian.