Where does belly button lint come from?

Clothing fibers

It comes from the belly button fairy. If you put it under your pillow, the belly button fairy will collect the lint and leave change.

There's a lint fairy, kinda like the tooth fairy, but instead you put money out and the lint fairy comes and puts lint in your belly button...👌

I'd also say from too much masterbation

Sinnin lots and lots of sinnin

The belly button

Same place as Lindt chocolate, I imagine.