The act of shoving a muffin (or muffins of any flavour) up a gaping, yawning sphincter. In some circumstances, this is repeated until no further baked delight is phsically capable of entering the tortured, distended shitchute, even after a good ramming with a broomhandle.
What could we do in this year's Talent Show? I dunno, luv, how about we try the "muffins up yer dirtbox" routine? That went down well at your mum's 80th.