Desmanchar is a versatile verb that can mean 'to smudge', 'to undo', or 'to fade'. It's an interesting choice because it evokes a sense of something coming apart or losing its form.
In the context of Seu Jorge's
Seu Jorge borrows the title from David Bowie and then writes something entirely his own in Portuguese. He is talking to someone who cannot decide whether they are coming or going, who follows foreign fashion, who got something wrong and is now claiming to be very zen about it. He is unbothered by their money and unbothered by the pose. The makeup will come off eventually, he says, and then the fear underneath will show.
The second half turns into a football commentary. Nil-nil, you left a gap, so I score. You won, come by tomorrow and pick up what is yours. It is short, sly and delivered with a shrug rather than a shout, which is the point: being a rebel here means dropping the act, not buying the right outfit. The phrasing is loose and very Brazilian, so it is a good listen for casual expressions like deu mole and na onda.