It's bringing up an entirely unrelated topic as some sort of "gotcha". Cigarette taxes were not part of the GGP's comment. I.e. a red herring

> The communication intent is often to distract from the content of a topic (red herring). The goal may also be to question the justification for criticism and the legitimacy, integrity, and fairness of the critic, which can take on the character of discrediting the criticism, which may or may not be justified.

> It's bringing up an entirely unrelated topic as some sort of "gotcha"

Expecting people to be consistent, and treat similar situations similarly, is not a "gotcha". Challenges like this are raised exactly to hold people to their own standards and question whether they are really okay with the consequences of what they just said.

The topic described is not at all "entirely unrelated". There is a clear natural category which encompasses both tariffs and cigarette taxes.

No, it’s not whataboutism. The original comment made a single argument: regressive taxes are bad. I provided a counter example: the cigarette tax is an example of a regressive tax that is good. This invalidates their argument. That doesn’t mean their position on tariffs is wrong, but they’ve provided an insufficient argument to support their viewpoint. There’s also an implicit corollary that they don’t fully understand tariffs if this is their position.

Whataboutism would be something like someone from the US arguing that China’s treatment of Uyghurs is bad, and someone from China countering with “well, what about America’s treatment of Native Americans?” The Native American argument isn’t a counter example of the Uyghur argument. Both positions can be true. It’s unrelated. That’s not the case here. You can’t be anti-tariff purely because it’s a regressive tax and also be pro-cigarette tax.