I think that there are many acts that can be seen as passive aggressive behavior, and sarcasm can be one of them. I think it would be considered passive agressive if the sarcasm is very subtle and not obviously snarky, but continues simply to annoy the other person, rather than just telling the other person what the real problem is. Sarcasm can also be passive aggressive when it’s kind of subtle, but the person making the remarks is constantly trying to make it seem like the situation isn’t particularly bad or that they’re just trying to be polite by pointing out something to the other person, even when it is clearly sarcastic. The real problem might be that they don’t like the other person, or they think the other person is stupid, or they think that the other person is just wrong (most of the time) or they just don’t have much care for the other person, like they just think the other person has little importance to them, but they don’t want to get into that kind of a conversation withe the other person, because it might deteriorate into something really ugly.
Generally, I think passive aggressive behavior involves saying one thing to a person, to appease them temporarily, whilst never meaning to do what one says.
Another example is withholding affection, on purpose, when you know your SO, spouse or whomever, really wants/needs it, because one is lazy, trying to teach the other person “a lesson” or doesn’t feel the same degree of emotional attachment, but doesn’t have the decency to tell the other person that they’re “Just not that into you.”
Another example is when someone asks another person to do something, like a mother asking a teenager to take out the trash, or a wife asking her husband to please pick up after himself, or a friend asking to make plans with another friend, and the people being asked, keep saying that they will do it, but then they never do.
Another example is when one person has asked another person to stop doing something that they find annoying or offensive or something that makes more work for the first person, but then the second person says OK, but then they keep on doing it, but then try to suggest that they aren’t doing it.
Another example when a perfectly able bodied person (not someone with a mental incapacity or memory problems) conveniently forgets things like schedules, birthdays, what the other person has said to them, to pick up something from the store, to start or complete a chore, simply because they don’t actually want to do the chore, but instead of telling the other person that they’re not going to do the action or follow the schedule, they just pretend that they forgot about it.
Another example is when one person regularly breaks “dates” (however you choose to define date) with the other person, but doesn’t give any good reason for why the date or activity needed to be cancelled other than giving some vague reason. Same thing with constantly taking phone calls whilst one is with another actual live person.