It is normal to have a celebration on your birthday
Mike is socializing with friends and it is Mike's birthday.
Mike wants not make a big deal of his birthday.
Mike asks his friends to keep things quiet but suggests they buy a round of drinks since it is his birthday.
Mike excuses himself from the group and goes home without telling them.
Mike's friends have fun celebrating their friend's birthday.
Mike's friends are left wondering what is wrong with their friend.