Squid, kinda funny but probably not to you. Don't feel bad tho as I'm sure this thread will attract many stories of dumb arseness. Here are two.
I made a grapple hook out of rebar to remove some x-mass trees. It worked great for three trees and then my boy scout knot let loose. Still in there.
A friend and I borrowed another friends pontoon with the stipulation that we added anchors to the pontoon. We did but my friend forgot to tie the anchor rope to the pontoon. A 25 ft rope does not do any good in thirty ft of water even if secured to the pontoon. Yeah, you guessed it, all my friends are brainacks, especially the guy who loaned us the pontoon.

Do nature a favor, spay/neuter your pets and any weird friends or relatives.