So did you know about this policy beforehand? It seems like you/your friends just need to learn to respect boundaries to be honest. If you know something will upset someone you probably shouldn't do it, even if it wouldn't upset you if it happened to you.
It does seem like an overreaction over something small but maybe he has professional contacts or family members on facebook who wouldn't understand or maybe it would at least cause him unnecessary embarrassment?
If someone has specifically requested something not to be done and then you go and do it, it's harder to see it as just teasing.