What does Boxing Day have to do with boxing?
1737, "disturbance of regular order," from French dérangement (17c.), from déranger (see derange). Of mental order, from 1800.
derangement de·range·ment (dĭ-rānj'mənt)n.
Disturbance of the regular order or arrangement of parts in a system.
Mental disorder; insanity.