Boche (n.)
1914, from French slang, "rascal," of unknown origin, applied by soldiers to Germans in World War I. Another theory traces it to French Allemand "German," in eastern French Al(le)moche, altered contemptuously to Alboche by association with caboche, a slang word for "head," literally "cabbage" (compare tete de boche, French for "German" in an 1887 slang dictionary). All the French terms are no older than mid-19c.