Agreed. A good joke has a punchline, it isn’t simply being annoying.
When I was giving guitar lessons, if I’d gotten a request like this I wouldn’t have bitten anyway. Not that I necessarily would have thought it was a joke (newbies coming in with unrealstic expectations of how fast they can learn is commonplace), but I would have just said, “no way. Can’t do it. That’s not something a beginner can do in a week. I’m sure we can work out something you can play, though.” I think that’s the way most instructors would react. I can’t imagine that many, if any, are going to knock themselves out trying to do something they know is impossible.
It kind of begs the question, if you can learn a complicated song by yourself without instruction, then why are you paying a teacher?
I guess I’m still confused. You sound like you can play pretty well (your ‘punchline’ is to kill on the song you just learned), yet you indicate you’ve always wanted to learn guitar anyway.
Huh?
mmm
I can see you’ve never had a lesson. 
A guitar instructor is never going to sweat your failure to learn a song. It’s a part time gig for a lot of them and they’re not salespeople. On the off chance he fell for it and tried to teach you a complex song in a week, all he’s doing is showing you the song. If you can’t master it, that’s your problem, not his.
And I agree this is not amusing.
That sounds really stupid and unfunny. If you have to do it, I suppose a Paganini Caprice would do. They are insanely hard to play.
I agree with Dio and Marley. One of the first things that a teacher is going to find out about a student is what level they are playing at already. Even if you successfully fool him into thinking that you play at a lower level than is true, which is harder to do than you might think, there’s no way that the apparent impossibility of your goal is going to cause him any sweat. When I have had students ask me to teach them how to play Eruption or something like that, I would tell them that the whole thing was beyond them (and me) right now, but here are some pieces of it that sound cool and are attainable. If the student insisted that he wanted to be taught the entirety of something that was beyond his current reach, I would show him the parts and tab them and revisit it whenever he wanted, but it would not cause me any sweat.
And this is really not an amusing idea at all.
Kim o the Concrete Jungle - There are lots of reasons to go to a teacher. Saving time learning songs and avoiding improper techniques are two that would apply to someone who can already play pretty well.
Go to YouTube and punch up Chris Broderick’s* segment from Guitar World’s “Betcha Can’t Play This” Tell him that’s what you want to learn, it’s only like 10 seconds long, how hard could it be?
*Fun fact - Chris Broderick seems to have three hands and 26 fingers.
Dragonforce: Through Fire and Flames.
A bit obscure, maybe, but it got a lot of popularity from being “that Guitar Hero song that’s really hard to play.”
I think a guitar teacher would just laugh if you told him you were a newbie and wanted to learn that in a week. Or a year. 
Or outside of a multitrack studio…
Stairway to Heaven. Because every nub who’s never held a guitar wants to be able to play that song. It’s a very stereotypical in-joke.
Ask them if they can play “far far away”.
Let me see if I understand this… you actually want to take lessons from the guy and learn to play, but you want to make it “funny” by being really annoying the first day? I don’t get how that’s funny. It’s just going to make you look like an idiot. He’s not gonna be sweating at all.
This prank’s gonna go over like a lead zeppelin.
mmm
Dude, you’re a dick 
It could work, but all people I know who teach music take their work pretty seriously.
I’d go with Communication Breakdown or maybe Eruption – or how about a super straight cover of 'Hideaway" (either Freddie King’s or Clapton’s).
I want a report back – it could end with you in a pine box or with a giant grin on your face.
I too am wondering how this prank is really going to play out.
cptsquid: Hello. I don’t play music, but I need to learn “Total Eclipse of the Heart” by tomorrow
hapless teacher: But…but…that’s impossible!
cptsquid: Nonsense! I’ve listened to twenty times a day growing up. It should be a snap
::sweat pouring down his brow:: hapless teacher: well…ok. I…well…suppose I could try. Once more into the breach, as they say.
cptsquid: HAHA! It is I, Captain Squid! And I really don’t need lessons at all. You just got Inked!
hapless teacher: oh dear me. However did I fall for that? Mercy, I need to sit down and have a hot cup of Earl Grey to calm my wits. You did get me. You got me good, good sirree.
Set up a camera, put it on YouTube and I’ll gladly be one of your ten viewers.
Can “You just got inked!” be the new “graped by the grapist”?