Perhaps in the fanfiction, Penny discovers she's pregnant right when she gets a big acting break. This would lead to a dilemma of choosing between her career and motherhood. The story could explore her internal conflict and how she ultimately decides. It could also show Leonard's support and how they work through it together.
One plot idea could be Penny struggling with how to tell Leonard. She might be worried about his reaction and how it will change their relationship. Another could be the gang's over - the - top reactions and attempts to help, like Sheldon trying to create a perfect baby - rearing schedule.
Another plot could be Penny dealing with the challenges of her acting career while pregnant. Maybe she gets offered a role that she really wants but is worried about how her pregnancy will affect it. This could lead to some interesting drama as she tries to balance her dreams and her new family situation.
A plot could be that Bernadette finds out she's pregnant right before a big work project. She has to decide whether to tell her boss or keep it a secret for a while. It would be interesting to see how she manages both her career and the pregnancy at the same time.
One plot idea could be that Amy and Sheldon have to deal with all the chaos that comes with preparing for a baby while still maintaining their unique relationship quirks. For example, Sheldon might try to create a scientific schedule for the baby's development and activities, much to Amy's amusement and occasional frustration.
There might be a fanfiction where Penny is pregnant and she starts to feel really isolated because she's the only one in the group going through this. She misses her old life a bit, and the story could be about how she overcomes these feelings with the support of her friends and Leonard. It's very emotional as it deals with her internal struggles.
There are many possible fanfictions on this topic. One could imagine that in the fanfiction, Penny's pregnancy might bring a new dynamic to her relationship with Leonard. For example, they could become more protective of each other and start planning for their future as parents more seriously. It might also affect their friendships with Sheldon and the others. Sheldon, who is not always good with changes, might initially struggle to adapt to Penny being pregnant and the new baby in their lives.
There could be a fanfiction where Penny's pregnancy makes Leonard super nervous. He starts freaking out about being a dad and all the responsibilities. Meanwhile, the rest of the gang tries to support them in their own clumsy ways. It's interesting to see how the characters' relationships develop during this big life change.
One interesting idea is exploring the characters' lives outside of the show's main plot. For example, fanfiction might delve into Sheldon's childhood in more detail, like his experiences in school that made him the way he is. Another idea could be alternate relationships. Maybe a fanfiction could explore what would happen if Penny ended up with Raj instead of Leonard.
Another good fanfiction idea is to have Penny's pregnancy bring out a more nurturing side in Sheldon. He could start knitting baby clothes for Penny's baby using his 'logical' knitting patterns. This would not only be a cute addition to the story but also show a different side of Sheldon's character in relation to Penny's pregnancy.
As far as I can remember, there is no such Penny wedgie incident in The Big Bang Theory. The series was filled with different kinds of comical situations. For example, there were Sheldon's idiosyncrasies, Howard's attempts to pick up women, and Raj's selective mutism. But a wedgie incident for Penny just doesn't seem to be part of the storylines.
One idea could be a crossover with 'Star Trek'. The characters from 'The Big Bang Theory' could find themselves on the Enterprise, with Sheldon trying to understand the advanced technology there. Another idea is a crossover with 'Doctor Who'. The Doctor could arrive in Pasadena and interact with the gang, leading to some hilarious scientific debates. And perhaps a crossover with 'Futurama', where the two groups of characters explore different time periods and universes together.