Sometimes you think rappers might be rapping about something other than rapping, like The Genius here in "Liquid Swords":
I'm on a mission that niggas say is impossible,
But when I swing my swords they all choppable.
I be the body dropper, the heartbeat stopper,
Child educator plus head amputator.
But it's all just a metaphor for rapping. The next lines in the verse:
Cause niggas' styles are old like Mark 5 sneakers.
Lyrics are weak, like clock radio speakers.
GZA amputates your head lyrically. The "s" in "swords" is merely stylistic.
When rap is completely meta, just a pure feedback loop devoid of any story or lesson, the fun lies in the rapper's creative flourishes, the ornamentation on the perpetual motion machine. There are uncountable ways to say "I'm good (at saying I'm good (at saying I'm good (at saying...)))"
But even given rap's overwhelming self-referentiality, I was struck recently when I re-listened to the R&B song "Feels Good" by Tony! Toni! Toné!.
Here are the lyrics to the rap interlude.
Mosadies the Mellow, quite a nice fellow.
Met three T, hit a rhyme acapello.
They had the rhythm and I had the rhyme,
So then I hit it that one more time.
It worked out and then they worked it in.
Tony Toni Tone has done it again!
As you can see, nearly the entire rap (five of the six lines) is about the arrangement and recording of the rap. Explicitly. No fancy (s)wordplay of note. (Unless you count "it worked out" as brag-worthy braggadocio.) What I'm saying is, I think this might be the most pointless rap interlude ever.
Any other contenders?