Heinie (n.) Look up Heinie at Dictionary.com
also Heine, as a typical name of a German man, 1904, North American slang, from pet form of common German masc. proper name Heinrich (see Henry). Brought to Europe in World War I by Canadian soldiers (British soldiers called the adversary Fritz).
heinie (n.) Look up heinie at Dictionary.com
slang for "the buttocks," by 1930s, probably a contraction of hind end.