It is not about not knowing some topic. I am myself an average programmer on my best day and I don't expect candidates to be genius level thinkers. It is the lying, the making stuff up on the spot - like what are they thinking? The blatant arrogance and callousness towards the person/people interviewing them. How hard can it be to say "I don't know" or "I don't use this concept in my daily tasks, but let me try to explain from memory" or something like that?