I always refer to Rebecca Solnit's initial essay on mansplaining, whenever I'm making a conscious effort to "check myself" on whether or not I'm doing it.

Clearly, many individual women have taken it upon themselves to misappropriate the term "mansplaining" so that it has transformed into a go-to invective (like you've described, as a way to "shut down" dissenting viewpoints in conversation, once and for all) beyond the original scope of the point Solnit was trying to make.

Solnit's definition focused on men who engage in gendered behavior against women, talking down to women or offering unsolicited explanations to women under the flawed assumption that the woman is somehow INHERENTLY underqualified or uninformed.

When a man offers an explanation of something if his expertise level is indeed superior to that of a female conversation partner, and if she's already engaging him on the subject matter as part of consensual discussion, that ISN'T "mansplaining."

Swap the spots of a man and a woman, and you can similarly define (with accuracy) whether "womansplaining" is or isn't present in a conversation.