Would HBD be considered rude or informal?

[Saferloop]

HBD is NOT rude, but it is certainly informal. It is primarily used for ease of digital communication. Some people might feel it is not long enough or personal enough, particularly if it is for an emotional or significant birthday wish. Under these circumstances, it's preferable to write “Happy Birthday” with a thoughtful message. Context is important; use a fuller, more complete and meaningful greeting in formal relationships or on special occasions, not in friendships or online chats (HBD).