In a poorly written piece over at Boston Magazine we have An MIT researcher purportedly coming up with the most difficult tongue twister yet. Only it's not. Try to "annunciate"--as I said, poorly written--this:
Pad kid poured curd pulled cod.
As the commenters mention, there are far more difficult tongue twisters. And more fun, too. They provided some good ones.
I'm a mother pheasant plucker,
I pluck mother pheasants.
I am the best mother pheasant plucker,
That ever plucked a mother pheasant!
The big black bug bled bright blue blood.
The sixth sick sheik's sixth sheep's sick.