It is good (almost) every time when someone points out how you've been a jerk to them and that you managed to offend them, knowingly or unknowingly.
If you did it intentionally - congratulations, it just got acknowledged. Or, less commonly, if it was a mistake, still better. You can now take it as a fresh idea and try (or avoid, if your hate rating for the subject is much lower than the average value) it on others.
Messing with someone unintentionally gives a stronger impact.