All of my saved documents retain the initial attempts at each poem descending down the page, since I start at the top again with each fresh idea.  Looking back over them can be a bit like an archeology dig, seeing the different strata of ideas develop, either with gradual changes, based on the ones below, or a sharp demarcation line, indicating a complete change of tack.

Here's the final version of the poem based on the suggestion "oboe":

An oboe walked into a bar
And was cruised by a Spanish guitar.
She said, “Only six strings,
“And you're flaunting those things?
“You're close, but you're just no sitar.”


The punchline was given to me by my housemate, based on the below idea which I felt just wasn't snappy enough. 

An oboe walked into a bar
With a yearning to be a big star.
So a Djinn in the band
Gave a wave of his hand,
And the oboe became a guitar.


It was almost there, and on a different day I might have said "good enough" and published it, but it didn't quite get across the idea of "the only way for an oboe to be famous would be to turn into a more popular instrument altogether" in a way that felt both clear and funny.  (No offense, oboists!  I love oboes).

Still, it was an improvement on the original formulation, which was a bit hazy as to which character got transmogrified.

An oboe walked into a bar
And announced, “I shall be a big star!”
It so happen a Djinn
Had a wish to cash in,
And poof, he became a guitar. 

(Zildjian is a popular maker of cymbals for drum kits, so I think that's where the "Djinn" came from.  A little too subtle, I think...) 


Going a step backward in time, there are these variations on a theme comparing an oboe with a bassoon.  There were lots of great rhymes with bassoon, so I was sure I would get something out of that, but nothing coalesced.

An oboe, a sax, a bassoon:
Had a contest to make a gal swoon.
The first one was
The second was
And the last sent her over the moon.

An oboe is like a bassoon:
Both their timbres can make a gal swoon.
But the oboe


An oboe is like a bassoon
In the same way a knife's like a spoon:
The first one cuts through


An oboe is like a bassoon,
And a chipmunk is like a raccoon.
Both are smaller and shriller
And 


Finally, my initial idea was so compact that it didn't need more than just two lines.

An oboe has two equal reeds
Which is two more than anyone needs.