Let's see ...
Well, we can justify virtually anything through our characters' views on "dementia" or however they interpret roleplayers being silly or flat-out non-roleplayers, but that's kind of a different thing from what is "immersion-breaking."
My own threshold is pretty low. As a rule, if it doesn't come across as something people would actually do (and not just occasional oddballs, exhibitionists, or attention-seekers), it breaks my immersion. I usually try to recover my immersion either by ignoring it or by reinforcing my immersion into Aria's psyche by having her react, and strongly-- typically, with sharp-tongued disdain.