I’ve never dwelt on the slang usage of the word “whatever.” My oldest son used it a lot. The Wikipedia describes it:
Whatever is a slang term meaning “whatever you say” or “I don’t care what you say”. The term is used to dismiss a previous statement and express indifference. In the late 20th century and early 21st century, the word became a sentence in its own right; in effect an interjection, it is used as a passive-aggressive conversational blocking tool, leaving the responder without a convincing retort. Anything they do or say can simply be blocked by the retort of “whatever”.
So if someone wants to talk to me about how great Corsi’s book is, my reply will be “whatever.”
Corsi's May smear book dismissive indifference "whatever," Jerry