The Big Bang Theory Recap with Spoilers - The Celebration Experimentation

While walking down the stairs, Amy points out that Sheldon's birthday is coming up and asks her boyfriend if they could throw him a birthday party. Sheldon immediately runs away, leading Leonard to quip why they hadn't tried that trick before. When Amy, Leonard, and Penny head back to the apartment to look for their friend, Sheldon jumps out behind a couch to "surprise" them and says that's one of the many reasons birthdays are terrible. Amy asks why he doesn't like his birthday, so Sheldon explains that his childhood birthday parties were terrible on account of his twin sister and her friends. Penny says that he has friends now that wouldn't torture him on his birthday, so Sheldon agrees to let Amy throw him a party...but that she owes him big time afterwards.

At the comic book store, Howard asks what they should get Sheldon for his birthday. Leonard mentions that Sheldon told him about a sad birthday story about when his sister lied and told Sheldon that Batman was coming to their party. Leonard suggests that they actually get Batman to come to his party and asks Stuart for Adam West's phone number. (Stuart had tried to get West to come to the store for a signing, but failed when the actor asked about payment.)

The next day, the girls and Stuart prep the apartment for the party. Kripke arrives at the party and mentions Bernadette's pregnancy, which causes Stuart to point out that no one had told him about the big news. Penny yells at him that he can have a pity party after they finish getting ready for the real party.

Meanwhile, the guys drive to Adam West's house to pick him up and argue over who was the best Batman. West joins the argument with gusto, and convinces Leonard and Raj that he was the best Batman over Christian Bale. Howard asks West about Ben Affleck's upcoming stint as Batman, but West doesn't even know what a Affleck is.

Amy helps Sheldon put on his tie and says that he looks good in a suit. She then jokes about seeing him in a "birthday suit" later, but Sheldon doesn't realize that his girlfriend wants to have sex with him.

Leonard's mother arrives at the party and immediately make her son feel unimportant. What a great mother.

Penny texts Amy to bring Sheldon over, and he's so nervous and happy about seeing his friends he forgets to be an ass to everyone. In fact, he gets overwhelmed by seeing everyone and runs into the bathroom.

Leonard and Amy argue over who should talk to Sheldon, but Penny beats them both to it. Sheldon admits that he got overwhelmed and apologizes for ruining the party. Penny says that he didn't ruin the party (but Raj trying to the Electric Slide will) and says she's sorry that her sister ruined birthdays for him. Penny says that Sheldon's one of her favorite people in the world and if he wants to spend his birthday in the bathroom, she spend it there with him. Kripke interrupts the tender moment by saying he needs to use the mirror to check his hair because he thinks he has a shot with Leonard's mother.

Leonard runs into Leslie (who's been absent from the show for several seasons) and says that a lot has changed since they talked last. Sheldon comes out of the bathroom and apologizes to everyone again. Amy proposes a toast and Sheldon decides that everyone should give toasts in his honor. Some of the toasts (Wil Wheaton) are great, some are too long (Raj) and some are self-promotional (Adam West). Even Stephen Hawking phones in to "sing" him Happy Birthday! Penny finishes the toasts off by giving Sheldon a hug, which Sheldon admits he finds only "extremely irritating".

As everyone sings Happy Birthday, Sheldon blows out the candles to his cake. With the party over, Adam West brusquely asks who's going to take him home...thus ending the episode.