It's rude to laugh at someone for their singing voice.
Simon is trying out for a singing competition, with Tim as a judge, and it is not going well.
Tim wants to reject Simon.
Tim rejects Simon, but recognizes that he only has some small things to fix and recommends a voice coach.
Tim laughs at Simon's singing and makes fun of his voice.
Simon is able to fix his singing problems and wins the competition the next year.
Simon stops singing and no longer has confidence in the things he does.