One common theme is the growth of their relationship. Their friendship or potential romantic relationship evolving over time, with Penny helping Sheldon become more social and Sheldon introducing Penny to new intellectual concepts.
Another great one is 'Sheldon and Penny: Unlikely Friends'. In this fanfic, it focuses on the early days of their relationship when they were just starting to get to know each other. It details their initial misunderstandings, like when Sheldon didn't understand Penny's pop - culture references and how Penny found Sheldon's scientific rants both annoying and fascinating at the same time. As the story progresses, they start to form a unique bond that is different from Sheldon's relationships with the guys.
One appropriate topic could be their adventures in scientific experiments together. For example, they could be collaborating on a project where Penny's practical skills and Sheldon's theoretical knowledge combine in a comical yet productive way.
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.
Leonard would likely become even more protective of Penny. Their relationship would deepen as they face the new challenges of impending parenthood together. He might start to take on more domestic responsibilities, like making sure Penny has a healthy diet during her pregnancy.
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.
Imagine Penny cosplaying as a sexy character from a fantasy world. She might have chosen a costume inspired by an elven princess but with a more modern and alluring twist. Her long blond hair is styled in loose waves, and she has a tiara on her head. As she walks into Sheldon and Leonard's apartment, they are both in awe. She then starts to act out some of the character's mannerisms, like speaking in an elegant accent and making grand gestures. This not only amuses her friends but also makes her the center of attention at the little gathering they have.
A memorable moment was when they both participated in the scavenger hunt. They showed great teamwork and competitiveness, which was really fun to watch. They were able to use their different skills to try and win the hunt.
A lot of fanfiction could explore Penny's emotions during her pregnancy. She might be excited but also a bit scared. In the fanfic, we could see her relying more on Leonard for emotional support. And the gang could throw her a really special baby shower, filled with nerdy and fun elements, like Star Trek - themed baby clothes or a cake shaped like a scientific formula.