It's called prooftexting, and it's something my pastor has railed against constantly. He likes to quote the line from The Merchant of Venice: "The devil can cite Scripture for his purpose." Any number of things can be justified by pulling a random verse from the Bible without context and saying "aha, see? it's in the Bible so it's got to be right!"
The fact that Bobby cited Matthew 20:16 rubs me the wrong way for a more personal reason. Mild powerlevel, but I was never the most athletic when I was younger (my frail skeletal body couldn't keep up with my flesh-and-blood classmates), so I'd frequently come in last in any physical activity. When I heard this reading back then, it became one of my favorite Bible verses for that reason. Even if I finished last, I could reassure myself that "the first shall be last and the last shall be first," so it didn't sting so badly. It was only years later when I could comprehend the context of the reading that I finally understood the meaning. I'm still glad it helped me out back then, but I'm glad I know what it actually means, and I have new favorite verses nowadays.
Bob using that verse to justify his twisted revenge fantasies is much worse than my misunderstanding. Lapsed Catholic trained by Jesuit scholars my ass, I can guarantee the fat fuck never paid a damn lick of attention at all. Maybe if he had, he might be a modicum better at being a human being, instead of a perpetually angry mound of flesh.