"mighty" made so much more sense to me (in the initial interpretations i had running). figure that you're completely under water (or, in this case, mud), and the only thing you're able to keep above is one of your fingers...

"who are you to wave your finger?"
then "eyehole deep in muddy waters"

are you waving your finger underneath, in the muddy waters?
or is our finger the only thing maynard sees clearly (from above the mess we're in)???

but fatty? fat americans? i dun know about this one yet.
a curve-ball, it would seem.