One common theme is the 'opposites attract' dynamic. Since Penny is often seen as the more social and street - smart one compared to the nerdy guys in the show, a male OC might bring a different perspective that still plays on that contrast. For example, he could be an artist who is also into science, which intrigues Penny.
Some Penny x OC fanfiction focuses on the OC being a musician. Penny, with her love for music and performing arts, is drawn to the OC. They could start collaborating on a musical project together. Maybe the OC writes a song for Penny to perform, and through this process, they develop a deep connection. It's a fresh take on Penny's character and adds a new dimension to the Big Bang Theory universe.
One place to start looking could be fanfiction.net. There are often a lot of stories in the 'The Big Bang Theory' category that might include a male original character (OC) paired with Penny. You can search using relevant keywords like'male oc x penny' to narrow down the results.
Another important aspect is to make the OC have their own unique personality traits that complement or contrast with Penny's. If Penny is outgoing and the OC is more reserved but has a great sense of humor that Penny discovers, it can create an interesting dynamic. Also, showing how they communicate, like the OC being a good listener when Penny vents about her acting career problems, can build a believable relationship.
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.
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.
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.
A male OC could be a new neighbor who moves in next to Penny. He's a fitness enthusiast and tries to get the guys to exercise more. This would be really funny as they are all so into their academic and nerdy pursuits. He might challenge Howard to a push - up contest or try to get Leonard to go running with him.
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.
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.