A graduate student at my University had an issue with a crow where he used to live. Whenever he went outside his house a crow would just swoop in at him and freak him out. He said he didn't get why it was doing that because there was no nest nearby. I told him that crows have are quite intelligent and even for animals as smart as they are, they have a well developed sense of humor. So instead of being aggressive, the crow might have been doing it because he thought it was funny when you freaked out. The student looked around and said "oh that's even worse!".