In the age of the internet, where everyone is anonymous and nothing is real, in character has taken on new dimensions. I've encountered a few spaces on Reddit that are as a rule always in character. The subbredit r/nosleep is probably the most popular example of this. r/nosleep is dedicated to creepypasta but as a rule all responses are supposed to treat the stories as true. This creates the interesting dynamic that not only do all threads start with a bit of performative fiction but that performance can continue into the responses with others relating it to their experiences or offering advice, condolences, or condemnation to the fictive writer of the story.
Improv is probably humanity's oldest art form. The first use of imagination is to envision oneself in a different place, under different circumstances and try to work out the consequences from their; either to achieve or avoid that scenario. The second use is to imagine being someone else. When we try and do this for people who don't exist you're essentially engaged in fiction. Kids do this reflexively as a part of play, adults don't really lose this feature but it becomes less acceptable as one grows up. Still, people love their fiction, it teaches experiences in the same way that non-fiction teaches facts, and many are ready to drop into a new role at the drop of a hat. It's interesting that we as a species are all actors to greater or lesser degrees.
IRON NODER: WE'LL RUST WHEN WE'RE DEAD