de facto segregation (noun)

1. The school had de facto segregation, with students naturally separating themselves based on their interest in different anime genres.

2. Although there were no official rules, de facto segregation occurred in the library, with readers instinctively separating fantasy books from other genres.

3. At the comedy club, there was a de facto segregation of comedians based on their preferred types of jokes, with pun enthusiasts naturally congregating together.

4. In the book club, de facto segregation emerged as members of the club unofficially divided themselves into separate groups based on their favorite types of science fiction novels.