I'm not sure which specific stories you are referring to. There could be fictional tales, perhaps in some very strange or niche genres. It might also be part of a local folklore or a made - up anecdote.
If these are part of a cultural or literary context, we would need more background information. For example, in some ancient myths, physical abnormalities in characters often symbolize something special, like a connection to the divine or a sign of a curse. Without more details, it's hard to fully understand the significance of a man growing big nipples in these stories.
There could be various interpretations if such stories exist. Maybe it's a metaphorical story about a man experiencing some kind of abnormal growth which is represented by the big nipples. Or it could be a humorous or horror - themed story, depending on how it's told.