May have multiple meanings:

1. When describing a stupid person, or
2. When describing a very large rain storm.
1. You're so dumb you couldn't pour piss out of a boot with the instructions written on the heel!

2. Look at those clouds, its about to pour piss out of a boot!
by 7h0rn3 April 5, 2009
Get the pour piss out of a boot mug.