Example sentences from the web:

• Boy: I am exhausted today. Looking forward to going home and doing nothing, hopefully, you’re up for the same?
  Girl: Yeah, whatever.
• Whatever. It’s like you want to get your heart broken again.
• Whatever… just another reason we made the right decision.

An interesting discussion on this topic: When did “Whatever.” begin to be used as a sentence?

Notice that ‘whatever’ has other meanings. It can be used as an adverb, a conjunction, a determiner, or a pronoun.
As a pronoun it introduces a relative clause and its meaning is: ‘everything‘; ‘anything that‘. For example: Do whatever he asks you to. As an adjective, it means ‘of any kind‘; ‘in any amount‘; ‘no matter what‘. For example, I saw no point whatever in continuing. Furthermore, we use it in questions as a synonym of ‘what’, but with more emphasis. For example: Whatever do you mean? = What do you mean? ‘Whatever’ is also used as a conjunction. In this case, it connects two clauses: I won’t go there, whatever he says.