The Absolute Worst Thing Penny Has Ever Done On The Big Bang Theory

Penny was a Big Bang Theory staple from only a few minutes into the pilot episode way back in 2007, and remained a prominent character on the show until the finale in May 2019. Initially just a friend to the group of lovably nerdy scientists, Penny (Kaley Cuoco) later dated and married Leonard Hofstadter (Johnny Galecki), and, in her capacity as the only non-genius in the group, often helped the guys navigate social situations — something they regularly needed from her. But although she was a beloved part of the group and came in handy during those social encounters, Penny wasn't always particularly nice about it.

Throughout The Big Bang Theory, fans learned that Penny hadn't always been a good person. On a number of episodes, it was made very clear that in high school Penny was not only part of the popular crowd, but also a bully, pulling awful pranks on people that were just plain not funny to her victims or her friends. One episode in particular saw her phoning some of the people she had bullied in her past and trying to apologize for her actions. In one particular instance, her behavior had been so inexcusable that one girl had flat-out refused to forgive Penny at all.

While Penny had improved drastically as a person by the time audiences were introduced to her on The Big Bang Theory, streaks of her nastiness and selfishness still shone through on occasion.

One episode of The Big Bang Theory featured Penny making fun of Bernadette (Melissa Rauch) to Bernadette's boss behind her back — something that you wouldn't do to people whom you consider friends, and especially not with their boss. On early seasons of the series, before she got a job as a pharmaceutical sales rep, Penny mooched off the guys on an almost daily basis, eating their food and using their Wi-Fi with no indication whatsoever that she ever paid them for it. (In fact, it was a running joke on the show that Penny didn't, even after her significant salary increase with the new job.) Penny also mocked the guys for playing video games and collecting comic books and figurines, with her constant joking getting so bad at one point that she guilted Leonard into wanting to sell all his collectibles after screaming at him for his hobby. The final season even saw Penny disclose to her husband that she actually never wanted to have kids with him, years after getting married with no prior word on the subject. 

But by far the worst thing Penny ever did on The Big Bang Theory did was her regular bullying and taunting of Sheldon (Jim Parsons). 

Sure, Sheldon was often a frustrating person to be around, but, while it's never discussed on the sitcom, Sheldon could fall on the Asperger's scale, according to Big Bang Theory actress and neuroscience Ph.D. holder Mayim Bialik. He struggles tremendously to understand social situations and customs, and sometimes has no idea that his actions aren't acceptable — behaviors that are consistent with Asperger's. Even though Penny is well aware of Sheldon's situation — and, being someone who has street smarts, should have been able to better identify his difficulties — she constantly teased him during their interactions.

Sheldon has clear anxiety when it comes to social situations, and while Penny is occasionally quite sympathetic, she often has no patience, lashes out at him, or calls him names instead. "Dr. Whackadoodle" is one of her favorites, along with regularly calling him a "big baby" when he gets upset about a minor inconvenience.

Knowing how Sheldon likes things a certain way, Penny regularly put him into situations that she should have known would make him uncomfortable. Early on, when Penny and Leonard had just started dating, she admitted to Sheldon that she lied to Leonard about finishing community college, expecting Sheldon to keep the secret despite knowing it wouldn't sit well with him. Sheldon became so distressed during the episode that he wanted to move out of the apartment he shared with Leonard, knowing being in close proximity with his roommate would force the secret out of him eventually. On another episode, Sheldon learned that Penny was considering breaking off her relationship with Leonard, and she again swore him to an uncomfortable secrecy.

Penny is also aware Sheldon doesn't drink, but during the first season of Big Bang, she decides to spike his drink to get him drunk, hoping it will make him less insufferable and provide her some amusement at the same time. This is a clear disregard for the fact that he doesn't want alcohol in his system, and in the real world would get her into serious trouble. The series didn't show any fallout from her giving the unwilling Sheldon alcohol, but realistically, if you had a steadfast rule that you weren't going to drink, finding out a supposed friend had basically force-fed you alcohol would likely result in a considerable argument.

During the Big Bang Theory episode where the men head off to a conference, Sheldon has to do something that makes him extremely uncomfortable. After realizing he left behind a flash drive with a paper he wanted to show another scientist at the conference, he phones Penny and asks her to get the flash drive and send it to him. But in order to do so, Penny will have to go into Sheldon's bedroom. Sheldon has never been comfortable with letting anyone else into his bedroom, so asking Penny to exactly that is a very difficult step for him.

Instead of realizing this and being sensitive about it, Penny ends up finding a letter from Sheldon grandmother. She proceeds to read it, then teases Sheldon mercilessly with the nickname his grandmother gave him, causing him to almost have an anxiety attack on the train because he can't convince her to stop. Leonard eventually has to step in and talk her out of her teasing, but it takes even him a few tries to get Penny to cease her taunting.

All in all, Penny seemed to take an almost cruel pleasure in flouting the rules of friendship when it came to Sheldon, especially early on in their relationship. While she often showed a softer side of herself — for example, on the episode where Sheldon had an anxiety attack over having a birthday party, Penny offered to just sit with him on the edge of a bathtub if that's what he needed from her — this wasn't the status quo when it came to their interactions. Penny, who has a much better understanding of social situations than Sheldon, should have been able to find a better way to deal with Sheldon's anxieties in a way that could have calmed the situation rather than exacerbated it.

Fortunately for fans of The Big Bang Theory, Penny did grow throughout the show, and became a close friend and confidant to Sheldon. She was often the only one who could comfort him and talk him off a ledge during the later seasons of Big Bang, and viewers got to see her find ways to cope with Sheldon and his quirks in less unkind ways, realizing that her behavior towards him was often hurtful. The result was Penny becoming a much better friend to the super-smart physicist (as well as the rest of the group) as the show went on, but she every so often still resorted to her teasing, making it difficult to say how good of a pal she really was.