It can be a form of performance humor at someone's expense, so the two situations you're referring to aren't always exactly the same.

I have no comment on how often claims to just be trolling are legitimate or the benefits of trolling and generally encourage relying a lot on the specifics of a given situation rather than looking for general principles with things like this. Plausible deniability is a double-edged sword.

It depends. To take an example, is it better to act prejudiced for a moment in order to elicit a reaction from someone, or to be a genuinely prejudiced person? The latter implies a significantly greater amount of harm over time. The former can be taken in good fun, or can be used to reveal a contradiction or other problem with the target's thinking. The harm from trolling tactics often outweighs the good, but the harm from holding and acting upon the harmful beliefs themselves is usually worse.

I think most people intuitively understand that the aggregate of behaviors stemming from a joke in poor taste are usually not as bad as the aggregate of behaviors stemming from actually holding poor-taste beliefs. This is why people who actually hold poor-taste beliefs often use the excuse that they are just joking. Of course, the reason they often don't get away with it is that the belief that trolling tactics are generally an acceptable way to conduct oneself is itself in poor taste, because it also causes more harm than good (and reflectively, because it could otherwise be used to justify harmful actions).

If the scenario is restricted to just an individual act by itself, then you're essentially asking, "Is it better to cause harm, or to cause harm and then also derive glee from it?" The latter seems worse to me, despite the fact that one of the two people in this situation is having fun. But the reason it can be judged worse under utilitarianism is because of what the perpetrator's state of mind implies about the perpetrator's likely future actions. (In real life, the broader context is always applicable.) But for the former, we have ignored or assumed away the perpetrator's state of mind. Perhaps in the former case, the perpetrator derives no glee but will hurt many more people.

So it depends. On average, it's a soft yes, but it may not be a good idea to strongly signal that to would-be perpetrators.

@Haiku that's a really interesting possession and one that I hadn't thought of before you mentioned it. However, I was thinking of trolling as more than ethically neutral behavior. I know that's a hot-take so please let me explain.

1. When I say trolling is an ethically neutral behavior I'm referring to trolling as behavior that is intended to provoke, prompt, or elicit a response from the subject. In my opinion, it is possible though not common to engage in trolling him in a way that society would deem beneficial. For instance, pretending to be technologically illiterate well on the phone with a computer scammer is something that I would consider trolling however, I would also argue that it is a benefit to society as it wastes time of people who intend to do more harm. To be very clear I'm not arguing that trolling is often or even mostly done for good however I think that at least for the purposes of this poll considering it as an ethically neutral behavior makes more sense.

So, I think the question comes down to is engaging in a specific act for the sole purpose of provoking, prompting, or eliciting a specific response (generally frustrating) response from another person is better than engaging in that behavior out of an authentic desire to do so.