The Bachelor Party Corrosion Season 9, Episode 3 -  Aired October 5, 2015

The Bachelor Party Corrosion

When the guys head off to Mexico for the weekend to celebrate Leonard's marriage with a belated bachelor party, their science skills are put to the test when their van gets a flat tire. Meanwhile, the girls enjoy a low-key bachelorette party for Penny, which leads to her finally telling her family that she eloped with Leonard.

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Guest Stars: Keith Carradine as Wyatt

Writers: Dave Goetsch (Story), Jim Reynolds (Story), Jeremy Howe (Story), Steven Molaro (Teleplay), Steve Holland (Teleplay), Eric Kaplan (Teleplay)

Director: Mark Cendrowski

Viewers: 15.4 million Households Rating: 10.1/16 Adults 18-49 Rating: 3.9/13

Available on iTunes

Episode Notes

  • The title refers to the corrosion method the guys used on the lug nut as they tried to replace the van's flat tire, which ultimately ruined their planned bachelor party.

> Relationship Agreement

According to Amy, Sheldon put a clause in the Relationship Agreement forbidding plastic surgery unless it's to look like a Klingon.

> The Simpsons

When the guys get a flat tire in Mexico, Sheldon worries, "What if it's banditos shooting at us? What if we get kidnapped? What if we end up in a factory making Bart Simpson piñatas for the rest of our lives?

Episode Quotes

Penny: What are you doing back?
Leonard: We got a flat and couldn't get the tire off.
Penny: Oh, I'm sorry.
Leonard: Thank you.
Penny: If it makes you feel any better, I pierced Amy's ears and her mom made her sit in my closet.
Sheldon: We blew up Feynman's van.
Penny: My dad killed my pig with his tractor.
Leonard: I spent the night in Mexico with Sheldon.
Penny: You win.

Amy: Uh, well, actually, to be honest I haven't told her yet.
Penny: You've been giving me a hard time and you haven't even told your mom about Sheldon?
Amy: I'm feeling a little dizzy from all the blood loss. I don't know what you're talking about.

Penny: Thanks a lot, guys.
Bernadette: What did we do?
Penny: Before I made that call, my pig was alive and happy and rolling around in the mud. Now he's illegally buried in our backyard next to my great-grandmother.
Bernadette: Really? They didn't eat him?
Penny: No! He was a beloved member of the family.
Bernadette: The breakfast meat family?

Amy: I know we're not making a fuss, but in the spirit of bachelorette parties, I made cookies in the shape of male genitals.
Penny: You really didn't have to- Whoa, that is anatomic.
Amy: Thank you. The veins are gummy worms.
Bernadette: Oh, look, Jewish and gentile.
Amy: I had extra dough.

Sheldon: Leonard?
Leonard: What?
Sheldon: I am getting too old for this crud.

News Stories

Title Date Posted
903 'The Bachelor Party Corrosion' Ratings October 6, 2015

The Big Bang Theory was Monday night's most-watched and highest-rated show after delivering a week-to-week gain in the ratings.  Full story

903 'The Bachelor Party Corrosion' Pictures September 23, 2015

We have added pictures from the October 5 episode of The Big Bang Theory, "The Bachelor Party Corrison", to our gallery. Keith Carradine reprises his role as Wyatt, Penny's father.  Full story

903 'The Bachelor Party Corrosion' Press Release September 21, 2015

CBS has released the synopsis for the October 5 episode of The Big Bang Theory, "The Bachelor Party Corrosion". Keith Carradine reprises his role as Penny's father, Wyatt, in the episode.  Full story


As Sheldon and Leonard eat in the kitchen, Leonard offers to give Sheldon a fun fact about mustard. Sheldon guesses Leonard's fact before he has a chance to say it. When Howard and Raj arrive, Leonard says they don't need to leave for the movies yet. Howard and Raj reveal that they're not going to the movies, instead they're "kidnapping" Leonard for a surprise bachelor party weekend. Leonard is excited and goes with them willingly, but Howard and Raj have to Sheldon up and carry him out of the building into the waiting van.

As they drive to their location, Sheldon is unhappy at being in the back of a creepy van. Howard explains that it's not just any van; it used to belong to noted physicist Richard Feynman. Sheldon's mood brightens as Howard explains that they're driving to Mexico to stay in the vacation house that Feynman bought with his Nobel prize money for a science-themed trip. Back in Penny's apartment, Bernadette wonders if Penny wants to celebrate her weekend by going to a strip club, but she's not interested. Even though they agreed not to make a fuss of the bachelorette party, Amy arrives with cookies in the shape of male genitals.

In the van, Sheldon is worried about Mexican customs and whether they're up-to-date on their inoculations. Back in Pasadena, Amy asks Penny how married life is treating her. Penny says it's good, though she's unhappy that Leonard hasn't worked up the courage to tell Sheldon he's living with her. After Bernadette wonders how Amy's handling being single, Amy admits she was thinking about changing her wardrobe. The girls are excited to hear that, though Amy says she decided against changing who is for some man. Still, Amy is interested in getting her ears pierced now she's no bound by Sheldon's relationship agreement, which forbids plastic surgery unless it's to look like a Klingon. When Penny offers to pierce Amy's ears there and then, Bernadette thinks the party has taken a weird turn.

Now in Mexico, Leonard tells Howard to slow down to avoid attracting the attention of the local police. Leonard is excited to be driving in a van that was owned by one of the greatest scientific minds of the 20th century, with the guys hoping some of Feynman's mojo will rub off on them. When there's a loud noise from the van, Howard thinks they've blown a tire, although Sheldon is worried the banditos are shooting at them. Meanwhile, Bernadette wonders why Amy hasn't updated her Facebook status to say she's no longer in a relationship. Amy realizes she should tell all her Facebook friends about her split, so she lets Penny know. When Bernadette asks Penny if she's updated her status to say she's married, Penny admits she hasn't even told her family yet. Penny says her dad always wanted to dance with his daughter at her wedding and she doesn't want to hurt his feelings.

Back in Mexico, the guys watch as Howard attempts to change the tire. He has managed to get four of the lug nuts off, but the last one is really stuck on there. Elsewhere, Penny finishes piercing Amy's ears. After Amy says her mother would lock her in the sin closet if she could see her now, Penny sees why Amy and her mom aren't that close. Bernadette thinks Amy would still tell her mother if she got married, annoying Penny who realizes Bernadette isn't going to let this go. After Penny decides to finally call her parents and let them know, Amy admits she hasn't told her mother that she broke up with Sheldon. Penny says she'll call her home now, but when she's done Amy is calling her mother.

When Penny calls her dad, she's surprised that he isn't angry that she got married without telling him. Wyatt tells Penny that if she's happy, he's happy for her. Wyatt goes on to admit that it's hard to tell someone something if you think it's gonna upset them, revealing that he accidentally killed Penny's pet pig about ten months earlier. Meanwhile, the four guys are all trying to unscrew the remaining lug nut to no avail. The guys realize that getting the lug nut off is nothing more than a physics problem. Following Archimedes' wise words, they set out to build a lever to help them - once they've decided on the proper pronunciation of lever.

Back in the apartment, Penny is angry with Bernadette and Amy for making her call her parents now that she knows her pig is dead. Penny insists that Amy call her mother and inform her of her break-up from Sheldon. As Amy makes the call, it's clear Amy isn't going to get to the news, so Penny grabs the phone from her. Penny not only tells Amy's mother about the break-up, but also the ear piercing and the penis cookies. Meanwhile, the guys' lever isn't helping so they look for another scientific solution. After an argument over which superhero would be best placed to solve this, the guys try to get the lug nut off with percussive shock, leading to a Queen sing-along. Next, they try thermal expansion by way of a tortilla chip. Then accelerated corrosion with burning salsa. Finally, they experiment with exothermic reaction with thermite created with rust and aluminium from the van. Soon, the van is completely alight.

When Penny leaves her apartment with a laundry basket, she runs into a rough looking Leonard and Sheldon arriving back home. As Leonard and Penny discuss the low points of their evenings, Penny accepts Leonard had it worse after he says he spent the night in Mexico with Sheldon.