Also, please no "tHiS iS eNgAgEmEnT fOr rEdDiT" comments. Would you rather have no such banner? As I'm not pushing anyone to become a long-term active user on Reddit, I don't see any benefit for the company from this. If you have a spare account, this may be a good cause to fire it up for a few hours.
The real point is doing something that gets attention. Buying beer just to pour it down the drain is dumb. Buying beer to make a video of you pouring it down the drain then posting that video to social media is protest. The difference is all about how many people see/hear you, and how many other people decide to join your cause.
Likewise, continuing to buy the product after all the protest is hypocritical showmanship, but buying a single 12 pack as a prop and never buying that product again for is boycotting. Keep in mind that the type of people who buy a case or two of bud light at a time are often the type of people who buy that much every week. If enough of those people switch brands, it might create a blip on on the company's radar at the very least.
Now my cynical point of view is that major companies no longer care very much about negative publicity. No matter how many shitty things the company does and no matter how shitty those acts are, people will still buy their product. Boycotting works on smaller companies because you can meaningfully impact their bottom line. That's rarely the case with massive corporations.