This is my headcannon. Nick’s bed wetting problem developed when he was younger after being picked on. Finnick found out about Nick’s problem and they used it as inspiration for their next big plan. Since then Finnick has developed a big brother attitude to nick never missing a chance to tease him when they are alone.
Draw and everything by familliar
Poor Nick it seems like Finnick like to tease him about his little night time problems.