According to Jim: Season 6, Episode 18
6 - 18: Jim's Birthday
Cheryl throws Jim an unwanted surprise party for his 50th birthday, which Jim then sabotages, and then later reveals the real reason why he won't celebrate his birthday.
Cheryl throws Jim an unwanted surprise party for his 50th birthday, which Jim then sabotages, and then later reveals the real reason why he won't celebrate his birthday.