If (say) you're starving to death in Donner Pass, then go ahead. Similar for drinking your urine - if at sea in lifeboat and dying for lack of non-salty water. Otherwise, violations of "eww, ick" social standards tend to be punished harshly.

It seemed really weird for a few years, when conspicuously talking to yourself went from being a "this person has a serious mental illness" indicator, to being a "this person has a cell phone" indicator.