Mostly pride/goofing around (he's a huge Weird Al fan, as well as a big karaoke fan), though he admitted before he started that there was no way he would get even a quarter of the way through the middle part.
The song was commissioned for the Michael Keaton Gangster-spoof, Johhny Dangerously. Which ... is actually a rather fun flick? I wound up watching it on a flight's streaming service, of all things. So that's fun.
The use of red spider lilies around the characters, and in the eyes of the protagonist, all scream “they are going to die.” Nice use of symbolism I wasn’t particularly familiar with. Red spider lilies, in Japan, symbolize funerals and death.
Before the second trailer, when I still had hope for the new Pet Sematary movie, I read the book for the first time in years and years. Now, having been a teenager when I read it originally, I just assumed the main character was an idiot...