I knew that crows were smart, but I had no idea that they are so smart that they could hold grudges for over 15 years. Not only can an individual crow hold a grudge against specific people, communication among crows is sophisticated enough that a group of them can share who to be wary of and continue to harass them for over 15 years.
Not that I ever planned to be mean to crows, but this is even more reason to be nice to them.