Is there an Appeal Against Authority fallacy?

See Dr Bo's answer.

I'd consider "this person is an authority, therefore they are wrong" to be a non sequitur (usually, some form of ad hominem fallacy).

Recall that the appeal to authority is defined as

Insisting that a claim is true simply because a valid authority or expert on the issue said it was true, without any other supporting evidence offered.

The opposite would be insisting the claim is false because a valid authority or expert said it was true. This really does not make sense because people who reject authority typically do so either because they don't agree that the authority is an authority (has expert status or is qualified) or does not agree with the rules in place set by the authority. There can also be other reasons.

An example is when someone argues that the medical community at large overwhelmingly agree that COVID vaccines are safe and effective, and one argues "This is BS because the medical community is all about profit." Notice that they are not agreeing that this is a valid authority on the issue; they are simply rejecting the authoritative status.

As you suggest, this is often done reactively and without evidence, so it is still problematic. It seems to be a overreaction or over-correction to the appeal against authority. For example:

Person 1: The COVID Vaccine is safe and effective because Dr. Fauci says so.
Person 2: Dr. Fauci is a media whore only interested in his own fame so the COVID vaccine is not safe nor effective.

While person 1 committed the appeal to authority fallacy, person 2 responded with unsupported claims and a general non sequitur . 

In summary, there is no Appeal Against Authority fallacy because nobody is likely to simultaneously hold that a person/group is a valid authority on an issue and then disagree with them. What they are likely to do is simply reject the person/group as an authority, and this can be for many reasons.