The story
From anal + expulsive. First use circa 1928; see quotation below. From the Freudian concept of the anal stage (roughly synonymous with toddlerhood), which says that children of toilet-training age who are liberally allowed to satisfy their fixation on anal expulsion (that is to say, to have “accidents” freely) eventually learn neither any self-control nor disgust for their own bodily waste, and their future personality is said to reflect that early upbringing via disregard for any social manifestation of order, control or organization, such as rules or tidiness. Compare anal-retentive.
Etymology from Wiktionary, CC BY-SA 4.0.