I have a co-worker who will answer every form of criticism with flat out denials, followed by his weird brand of excuse.

"Hey, dude, did you do XYZ?"

"Yup."

"Weird, because it isn't done."

"Can't be, I just did it."

"Ok, show me."

"Oh, it wasn't done. Weird. I could have sworn I did it. Must've been a mistake."

"Nope, I checked, you didn't do jack shit. Ever."

"That's weird because I usually do that, all the time."

"Okay, here are the logs proving you never did it."

"Oh, okay, weird, I must've overlooked it or forgotten it. I usually do everything the way it's supposed to be done."

"Alright, here are 200 examples of you doing it, every single one showing without a shadow of a doubt that you never did anything."

"Oh, okay. But normally, I would do it correctly every time."

"I'm done. Forget it."