Not all

Not all (also known as Not all X) is a turn of phrase that attempts to force unnecessary "nuance" into a subject that already has nuance, either by: The Not all fallacy is employed in the hopes of shutting down conversation by making the opponent appear to lack all nuance.
 * 1) Deflecting fully specific criticism by pretending it's actually quite unspecific (first form), or
 * 2) Insisting that you need not be specific yourself when dishing out criticism to others (second form)

Example
The first variant of the fallacy is when someone tries to deflect a specific example with a general blanket statement:

Example
The second variant of the fallacy, where Person A is at fault, instead denotes when someone tries to demand that a blatant overgeneralization not be questioned:

Not all men
"Not all men" is a specific form, and probably the most famous application of this phrase. It was coined by Twitter user sassycrass in 2013 but rapidly shot to fame after the 2014 Isla Vista killings in response to those who argued that Elliot Rodger's murder spree was being blamed on all men, instead of being the result of misogyny on Rodger's part. #NotAllMen became a shorthand to expose the "not all men" response, along with its many paraphrases, as a defensive knee-jerk reaction which just serves to derail conversations about sexism, and shift the focus from victims of sexism to a perceived but nonexistent slight to oneself, which is effectively a form of mansplaining.

However, in the rare case that the original complaint about sexism is indeed a blatant generalization which explicitly and unequivocally states something derogatory about "All men…", then this is the second form of the fallacy identified above, and "not all men" is a valid response.