I agree with BamaFan on her comments.
1. It is rude as a one word answer.
2. It tells me you have either not thought out your beliefs on the topic, don't care, or trying to end a loosing battle.
I will never forget a supervisor in my doctoral courses used it with me. We were debating a topic and he told me "whatever"; mind you this is a professional topic and there is a right answer and this professor could not backup his argument. I was horrified that an adult 20 years my senior would tell me "whatever" to shut me down. I am a very non-confrontational person and don't often try to defend a topic but I knew I was right! That was probably about 15 years ago and I still remember his response so clearly...
