To all rappers: shut up with your shutting up
And keep your shirt on, at least a button-up
Yuck, is they rhymers or strippin' males?
Out of work jerks since they shut down Chippendales

from MF DOOM – Beef Rapp Lyrics on Rap Genius

Meaning

In other words, shut the nonsense up (‘stop saying nothing’), keep your shirt on, this is rap not modeling. His point is that rappers walking around with their shirts off are basically Chippendale’s rejects looking for a paycheck in rap — “beefcakes,” as they are sometimes called.

But there is also a self-deprecating dig in here as — DOOM doesn’t have the kind of body that sells in magazines and album covers.

See, e.g.:

DOOM at Chippendales auditions, dramatization
http://www.metacafe.com/watch/5314739/chris_farley_patrick_swayze_as_chippendales/

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