It is rude to ruin someone else's birthday celebration.
Toms best friend lied to him about something small, and then invited him to his birthday celebration.
Tom wants to confront his friend about the lie.
Tom asks his friend for a private word at the party and asks why he lied.
Tom clings his glass at the birthday celebration and tells the entire party about his friend’s lie.
Tom’s friend apologizes to Tom, and explains that he lied in order to keep a promise to a mutual friend of theirs.
Everyone picks a side and is either upset with Tom or his friend, nobody has a good time, and his friend cancels the celebration kicking everyone out.