We are all clueless about many things.
But not all are clueless about all aspects of life and the universe.
Those who cling on to mythologies and angels, devils and astrology may well be the ones who are really clueless about the physical world.
I am not sure that all atheists are pretending to know the answer. There is no need to engage in unpleasant language towrds people we don’t agree with, even if we believe we have answers to ultimate questions questions.