it's fine if it's a character who is used to weird canon stuff like multiple universes, but if it's a relatively mundane canon then being fourth walled is like dropping a philosophical bomb about their place in the universe and who they are. it's not always fun to play out and some players who fourth wall people don't bother to stop and think about that. it's especially not fun when it happens at their first meeting or in an early game event or tdm and impacts their entire entry into the game.

in general i think it's a boring way of creating drama and shows a lack of creativity. if all you can think of is "lol you're a cartoon" i'd rather you stopped and thought of something else.