2. Something that cannot get any stupider than it currently is.
3. Bullshit that can't be broken down into simper forms of complex absurdity.
For example, pseudoscience.
"Creationism is a joke. It appeals only to the weak-minded and is simply an intellectually lazy excuse to be willfully ignorant of real empirical science. The irreducible stupidity of creationism and its advocates is simply unfathomable."
"That dumbass thinks the world is 6,000 years old and that dinosaurs once lived together with humans. He is so irreducibly stupid. Did he purposely fail high school biology, or did he get his so-called "facts" from a church? He is such a n00b."
"Anyone who can stare directly in the face of evidence for evolution and still have the audacity to ignore it has to be willfully uneducated—more accurately, irreducibly stupid."