I'm of the belief that pretty much any OC has some of ourselves in there one way or another, but I'm curious if other people have character traits that weren't intentional but just kinda happened due to things outside of their story / world / game / etc.
For example, in FFXIV, I used to use the /riceball emote (which has your character eat a rice ball, of course) regularly when I was waiting around, and my friends started joking about how rice balls were her favorite snack... so it stuck.
There was also a time when I, the person, couldn't remember the word "Hrothgar", so I ended up referring to all Hrothgar as the name of another friend's character. It then became canon that my character calls all Hrothgar by that name without realizing it.
There's gotta be other examples of this!