If it's for exposing hypocrisy, it's not whataboutism. If it's for exposing a flaw in one's argument, it's not whataboutism. If it is to deflect the argument from having to confront the truth about something, that's whataboutism.
ETA: whataboutism is a kind of logical fallacy. It's trying to say that because someone else did the same thing, the thing I (or someone I support) did is therefore dismissed.
That is all true and I agree with it. However when hypocrisy is exposed that way it is called whataboutism - usually by the hypocrite.