Funny how I'm only sick if you never catch a thing
Lupe is saying that he’s only considered a good rapper if there’s no meaning behind his lyrics, or the meaning is so subtle that no one can catch it.
Lupe’s also playing on the concept of being literally “sick”, i.e. his rhymes are contagious but you can’t quite “catch” them because they tend to be so complex
The line is also a response to those fans who think that anything less than a complex Lupe is not good, or not “sick”. In Lasers, Lupe has a more simple and straightforward lyrical style. That created some outrage with people accusing Lupe of dumbing it down. Lupe finds it funny that even though he has retained similar messages in his music, others still find his recent music to be inferior to his older music.
A lot of people claim he’s ‘sick’ because of his deep metaphors, etc. which aren’t understood at first i.e. when you don’t ‘catch a thing’
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