I thought she was coming to drop some stuff off, you know, then go right back.
If he asks about something in particular then explain it. He may not ask, the gags are funny without knowing the background and he deserves a chance to appreciate the movie more when he watches it again someday. If he’s really into it point him to the imdb trivia page.
My recommendation would be to get the movie on DVD so he has the option to watch the movie again with the in-character commentary track.
A modern audio standard in our digital age is still called “Dolby”, isn’t it? Else you’d have to explain that bit too.
And that Des Moines is not in Indiana.
I’m from Des Moines, and saw that movie many times for free because my brother worked there. Towards the end of its run, senior citizens were coming to see it and saying, “We have GOT to find out if this movie really is as funny as everyone says it is!”
BTW, at the time, some critics chastised Rob Reiner for making a feature-length doco about a movie nobody had ever heard of before, and there were indeed people who walked out halfway through saying, “Who IS this band? I’ve never heard of them before.”
I’m going to add that I have not been able to watch it ever since the news broke that the daughter of Tony Hendra, who played their manager, made very credible accusations that he molested her.
I seriously had people asking me whether this movie was a true story, about a real band* when it was new.
I’m like, even if you don’t recognize “the meathead”, don’t you recognize Billy Crystal? Patrick McNee**? Howard Hessman? I even think I knew who Fran Drescher was (maybe) at the time.
I admit I didn’t recognize Lenny (or was it Squiggy?), but I never liked L&S. And even more I admit I was surprised to see they wrote and played their own music.
Fun fact: Blue Oyster Cult played Magic Mountain when I lived in LA. I thought, “man, Spinal Tap is true! How the mighty have fallen.” AFAIK, they didn’t have a puppet show with them, though.
*to clarify, they didn’t think it was a biopic, they thought it was a real documentary
**eta: I found it funny that the guy directing Get Back was Michael Lindsay-Hogg, and then I understood Sir Denis Eton-Hogg.
You don’t even need to be familiar with Mozart or Amadeus to get that gag. 
Another vote for no prep-work. Dive right in.
“His music is made by ‘DJs’ and ‘producers’ sitting in front of a computer.” Maybe he would identify with Popstar: Never Stop Never Stopping.
Also, let him know there was a time, long ago, when Americans were convinced that any group from England was by definition if not immediately important, then at least must be tuned in to something we weren’t because, you know, from England.
I know it’s been decided already but I want to chime in and say I didn’t know any “back story” about the movie or the industry when I first saw the movie as a kid in the 90s. The movie holds its own. If anything, it made stuff funnier going forward.
I had to explain to an Non-American how it was possible to make a mistake resulting in something being 1/12th the size but apart from that, everything else translated.
He’s a completely metricated kid. He won’t get that one, either.
Odd personal factoid: although I’ve seen all of Christopher Guest’s other movies from start to finish, I don’t believe I’ve ever watched This is Spinal Tap in one complete viewing.
Because of the movie’s buzz, I’ve watched so many (various scene) clips of the film, so many times, I’m sure, patching them together, I’ve watched the movie in it’s entirety a few times over.
Has anyone else done this with TiST…or any other films?
This is the answer you’re looking for. Not only is it a great documentary, Anvil is as close to a real-world analogue to Spinal Tap as is possible. And one of the founding members is actually named Robb Reiner.
But even if you’re not going to show him anything beforehand, you should watch it yourself because it’s a really good doc for This Is Spinal Tap fans.
edit to add Anvil documentary trailer
Just here to point out that “These go to 11” isn’t really a rock music joke, it’s a maths/physics joke. Carry on.
Definitely, because 11 is one louder than 10. That’s just math!
No no no! You’ve got it all wrong! If I’ve told you once I’ve told you a hundred times- watch Spinal Tap first, and puppet show last!
Since it doesn’t look like it has to be a movie, how about the episodes of Documentary Now!, with Bill Hader and Fred Armisen. My favorite is Sandy Passage, a spoof of Grey Gardens (1975), or the 2009 version Grey Gardens (2009) with Drew Barrymore. It’s take some investigation on the backstory of these two ladies, but I think the ending is absolutely fantastic, especially how similar it is to The Blair Witch Project (is that an option?).
I tried to watch This Is Spinal Tap a few weeks ago, but it has never clicked for me, despite multiple attempts to view it. I have a hard time understanding the hard-metal rock world so I never understood why it was so popular.
I think it’s just a different sort of humor than you enjoy. Or that particular attempt at humor didn’t work for you (if you’ve enjoyed similar films). I was never into hard-metal but most of the jokes and events stand on their own: A dude trapped in an egg pod for the entire concert, the tiny Stonehenge, the Black Album and Smell the Glove issues, the girlfriend wanting them to dress in animal costumes, the puppet show, drummers dying, the Goes to 11 scene… none of these require inner knowledge of hard metal to land, they’re either sight gags or pretty universal in their ridiculousness. I’m sure there’s stuff to enjoy more if you’re “in the know” but think the film sets itself up pretty well regardless.