To fail miserably.

To fail so hard your undergarments are compared to that of a baby having massive diarrhea up their back.

To have the upper hand and completely suck. Hard.

<can also be used in other tenses>
Payton Manning blew the diaper. Hard.

Or

Payton Manning had a big ass diaper blowout in the Super Bowl.
by GalNasty February 3, 2014
Get the Blew the Diaper mug.