Q:

Usage of ça baigne

I've heard that the response "ça va" can be replaced with "ça baigne" (lit. "that bathes") in casual contexts. Is this a common greeting among friends, or something that simply exists but isn't commonly used? How does it feel compared to ça va?

A:

We can find the origin of the word in an article by l'Internaute :

Sens : Tout fonctionne bien. 
  Origine : Cette expression date du XXe siècle et prend ses origines sur les établis de
  bricolage. En effet, lorsqu'un mécanisme est rempli d'huile, il
  fonctionne bien et tout va pour le mieux. Ainsi, par extension, la
  formulation est employée dans le langage familier pour dire que tout
  va bien, que tout est sous contrôle.

"Ca baigne" is indeed familiar and used with friends and family. As radouxju said, it was mostly used about 10 years ago and it is hardly used nowadays, even if it's probably still used by youngsters. "Ça va" could be used with basically anybody in a non-professionnal scenario. You would use "Comment allez-vous ?" in that case.

