WMG: Casey and Andy

Bob is Jenny Everywhere's uncle

For one thing, Bob's "being there too" ability is similar to Jenny's "Shifter" abilities, to the point that any differences can be chalked up to Jenny's powers being explored more deeply.

Grover Cleveland has a vendetta against Andy because of the fortune-telller's prophecy that Andy would urinate on his (Grover Cleveland's) grave.
As Andy urinated on Grover Cleveland's grave because of Grover Cleveland's vendetta against him (Andy), that makes this a cross between a Stable Time Loop and a Self-Fulfilling Prophecy, since under the premise of the guess the fortune-teller scene happened before Grover Cleveland's "heh heh heh, I got you!" scenes.

Dilbert's garbage man is a parallel universe version of the Quantum Cop.
Unlike the typical "parallel universe version" guesses, this one is meant to be in-continuity. QC's parallel selves have canonically appeared in the non-cop occupations of Quantum Crook and Quantum Ninja, and he/they always wear(s) sunglasses to dull the details so he can look at the big picture after being "awakened" to his/their Quantum Cop state. The World's Smartest Garbage Man always wears sunglasses (even at night), always wears a hair-obscuring hat except when impersonating someone in a different job (a Girl Scout cookie mark for QC, Dilbert's delivery doctor in Dilbert: The Animated Series), and is disproportionately smart for his chosen line of work (not that being a garbage man or especially a cop doesn't require intelligence and quick thinking, but they would each do well in a science-based career, mad or otherwise). The WSGM's inventions definitely have a Casey and Andy style to them, which for QC originally resulted in his games against and knowledge of Casey and Andy, and most importantly, I always heard QC's voice as that of The World's Smartest Garbage Man.

Casey and Andy hacked hell

It been revealed a machine called the soul keeper keeps souls in hell, it even becomes a plot point that the real Andy would have taken it apart. So naturally, they have taken it apart, figured out how it works and that's why they keep coming back to life.

Casey and Andy made a deal with the Devil... before the comic

Although one strip is clearly labeled as when Andy first meets Satan, it definitely appears that he is doing rituals to attract her before the end of the strip (namely the sacrifices). They were doing some random but dangerous experiment, died, and negotiated a deal with Satan that they would always go to Hell and suffer for eternity after dying, but come back to life afterwards. The various judgement that they have to go through after death are just formalities. Andy was attracted to Satan during the process, but she forgot about him, so he had to attract her again. This repeated eternal torture drove them progressively more insane and gave them enormous amount of time to think about science, explaining most of their personalities over the course of the strip.