Memetic Junk
I heard a rumour once that some DNA is just along for the ride. It does nothing, but since the whole system's there to replicate, it replicates along with the rest.
Maybe memetics works the same way. Maybe every language has bits of crap, lying around, not doing anything. Perhaps jokes are memetic dross, hanging around without function, just because some contraction rhymes or sounds like a rude word.
Maybe internet-memes are a cancerous infection; a growth in the mind-space of humanity.