The Big Bang Theory Season 9 Episode 17
The Celebration Experimentation
Amy tells Sheldon she wants to celebrate his birthday by throwing him a party this year, but Sheldon doesn't like the idea at all.
He tries to change the subject, then admits that he doesn't like birthdays because of the way his twin sister's friends used to torture him each year.
The gang convinces him to have the party, saying it wouldn't be like that this time. Leonard, Howard, and Raj even decide to try to get the real Batman, Adam West, to attend the party to make up for a cruel joke that was played on Sheldon when he was a kid.
Everyone shows up to the party, including Wil Wheaton, Leslie Winkle, Kripke, and even Leonard's mother.
Sheldon is nervous before going in, but Amy makes him feel a little better. Still, when he gets inside, he has an anxiety attack and runs into the bathroom.
Penny goes to to talk to him, and finally convinces him to join the party in a heartfelt moment.
Everyone gives nice speeches to Sheldon at the party, then Amy has one more surprise -- a virtual visit from Stephen Hawking.
Everyone, including Stephen Hawking, sings Happy Birthday to Sheldon. This also marks a happy birthday for the show itself, reaching its 200th episode.