The story
Coined by analogy with come out of the closet, with the proverbial hiding place being changed to a broom closet, a jocular reference to stereotype of witches riding brooms.
Etymology from Wiktionary, CC BY-SA 4.0.
come out of the broom closet
Today it means: To publicly reveal that one is a Wiccan or some other type of neopagan. Full definition →