Yes. The conflicts between Sanji and Luffy in the manga often stem from complex circumstances and character developments that drive the narrative forward.
In RWBY fanfiction, the Weiss vs Winter fight can be a display of their different combat styles. Weiss is more about grace and precision with her Glyphs, while Winter, being more experienced, has a more refined and perhaps harsher style. Their fight could also explore their complex relationship as sisters.
Well, in a lot of fanfictions about Luffy vs Katakuri, Luffy's growth is depicted quite vividly. His growth can be seen in his improved observation Haki. He starts to anticipate Katakuri's attacks more accurately, which is a huge step forward. He also becomes more creative with his attacks. Instead of just using his standard punches and kicks, he combines different moves and even creates new ones on the fly. This shows that he's evolving as a fighter and not just relying on his basic skills. Another aspect is his mental growth. He faces a very tough opponent in Katakuri, but he doesn't give up. His resolve gets even stronger, which is an important part of his overall growth in these fanfictions.
Jealousy is a common reason. For example, if one wife has a more luxurious lifestyle or gets more attention from others. Another reason could be competition, like competing for a limited resource such as a particular job opportunity in a small community where their husbands work at the same place.
The "Negative Fruit" in One Piece was one of the superpowers that Luffy encountered for the first time in the story. The scene where Luffy and his gang fought against the "Negative Fruit" appeared in episode 598,"Luffy and Luffy!" Adventures in Two Worlds.
Jealousy can be a big reason. For example, if one mom thinks another mom's child is getting more attention or opportunities. Another reason is differences in parenting styles. If one mom is very strict and the other is more laid - back, they might clash when their kids interact.