jarhead (n.)youdaoicibaDictYouDict[jarhead 词源字典]
"U.S. Marine," by 1985 (but in a biographical book with a World War II setting), from jar + head. Also used as a general term of insult (by 1979) and by 1922 as a Georgia dialectal word for "mule."[jarhead etymology, jarhead origin, 英语词源]