#hbtm

What does "hbtm" mean?
HappyBirthdayToMe, happy_Birthday_to_me, HappyBeedayToMe, HappyBorndayToMe, HappyBdayToMe, HappyBDayToMe, HappyBirthdayeToMe, happy_birthday_to_me, Happy_Birthday_To_Me, happyBirthdayToMe, HappyBirthdayToME, HappyBrithdayToMe, Happy_Birthday_to_me, hApPy_bRdAy_tO_mE, HappyBirhdayToMe, HappyBirthdayToMoi, Happy_birthday_to_Me, happyBdayToMe, happy_birthday_to_meh, HappyBirthdayToMyself, HappyBirthdayToMy, Happy_birthday_to_me, HappyBithdayToMe, HappyBirthdayTooMe, HappyBirthdaayToMe, HappyBirthdayToMomz, HappyBitghtdayToMe, HAPPY_BIRTHDAY_TO_ME, HappyBirthdayToMeeeeee, HappyBirthdayToMeeee