Although Bob's reasons for revenge initially seem trivial, it is revealed that Alice has in fact wronged Bob in a more serious and justifiable fashion.
Bob makes it look like he murdered Alice's family as an elaborate practical joke.
Alice shoots Bob after he demotes her, but not on purpose: the gun was only meant to scare him.
Bob's planned revenge is still drastically over-the-top.
The staged murders are just the first step in an elaborate process of making Alice suffer psychologically.
Parodied: Bob attempts to murder anyone who accidentally throws a paper airplane at his head.
Zig Zagged: Bob plots to get Alice murdered after she gets him fired. He hires a sniper to shoot Alice. However, the sniper, Charlie, doesn't fire at the last moment because Alice is his girlfriend. Bob, seeing all this, knocks out Charlie and grabs the rifle. It misfires when he tries to fire at Alice, however, so Bob, in frustration, throws the rifle... at Alice.
Bob's revenge is entirely proportionate to Alice's offense.
In this factor, Bob plans to get Alice fired after she gets him fired.
Enforced: In Bob's culture and the story's time period, this escalating Cycle of Revenge is perfectly (and disturbingly) normal.
"You don't think that taking revenge to this degree is a little... excessive?"
Defied: "Seriously, what happened to me wasn't that bad; I'm not going to go crazy here."
Exploited: Diane uses Bob's psychology to send him after her enemies by tricking them into pranking him.
Discussed: "Ran into Bob yet? Well, be very careful, he set Charlie on fire for giving him scalding hot coffee once."
Conversed: "You have to wonder what those people who make overblown revenge plots are compensating for."
Deconstructed: Bob spends all his money and loses his job, friends, and credibility trying to get his disproportionate retribution. He probably fails, too, since the Rube Goldberg Device of a plot is likely to implode. And even if he succeeds, Being Evil Sucks and he realizes it cost him more than it was worth.
Reconstructed: Bob has serious repressed anger from being wronged in a way that does merit his over-the-top vengeance, and Alice just happened to be the straw that broke the camel's back.
Played For Laughs:
If you interrupt Bob, or express hatred for any of his favorite things, he'll kill you, but the victim will come back.
Played For Drama: This all results from a serious anger problem and a lack of understanding of consequences and what is proportionate; every time his little brother, sister, or son is picked on, a building goes down.