The story
From feminist + -splain. Compare mansplain, womansplaining.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: To explain feminist concepts or a feminine perspective, especially when done in a condescending manner or to explain something the listener already knows, presuming that he has an inferior understanding of it merely because he is male. Full definition →
From feminist + -splain. Compare mansplain, womansplaining.
Etymology from Wiktionary, CC BY-SA 4.0.