Une femme est une femme (Jean-Luc Godard, 1961)

Full of invention and humour (all the puns giving the subtitle writers a hard time for sure), but not sure if it really is one of Godard's most accessible films, as is sometimes claimed - the relentless turning of conventions against themselves without some sort of formal cathartic explosion (it actually keeps playing by its own rules throughout) means it is also one of his oddest films. And also probably one of the principle exhibits in the feminist case against him.