As a native speaker, I will try to answer without being pedantic with a dictionary: to be passive aggressive is to answer with an unusual assumption and to act like the other party should have known all along.

E.g. if you want someone to leave and it is snowing, say “I just cleaned off the snow from your car so you can make it home safe. When do you plan on leaving?” This places an expectation and social pressure to accept the gift of cleaning the snow by leaving soon.

E.g. if you want to leave work at 5pm daily and your boss knows this and adds a frivolous mandatory meeting to the office calendar. You can take notes in the meeting then at the end send the email to the recipients and say “this meeting could have been an email with no knowledge lost”. This implies that your boss did a disservice by wasting everyone’s time when they could have just used a secretary and an email and let you keep to your informal time to leave boundaries.

Good luck figuring out and understanding the actual definition!!!