system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the psychological reason why people who are close affectionately poke fun at each other?

Why does my best friend and I greeting each other with "what's up you fuckin' slut" draw us closer? By all accounts it doesn't make sense.
gpt
Aggression is playfully used right across the animal kingdom, so it is probably an inherited way of forming a relationship - some tropical fish (ciclids) fight through mouth-wrestling, and when a male and female are evenly matched, instead of the weaker fleeing from the stronger, they become mates for life and proceed to lay egss and raise a family.