The not so subtle art of Fragging first came to prominence during the Vietnam war. Here grunts (the US squaddie) took it upon themselves to relieve pish poor officers of their commands, commissions and lives by assassinating them. Given how poor or gungho some of the officers were in Vietnam, the grunts saw this as a form of self preservation.
Fragging was commonly done by rolling a fragmentation grenade into their tent or toilet and blowing them up. The term frag coming from fragmentation. This method left very little evidence as the grenade fragments could not be checked for fingerprints, there being no possible ballistics match and DNA testing was far in the future. Warnings were sometimes given using smoke or tear gas grenades.
Another popular method of removing an officer was a friendly fire incident during a firefight. In the heat of battle (especially in the American army) blue on blue incidents happen and were rarely given more than a cursory examination especially if the 'accident' happened on patrol. This was also a fragging as the term became accepted as the generic for the removal of an officer or indeed annoying fellow grunt.
At least 230 American officers were killed by their own troops and another 1400+ other deaths could not be explained during the Vietnam war. This tradition has continued to the present day in the US Army with several incidents having been reported in Iraq.
Historical Fraggings: It should be noted that incidents of fragging have been recorded as far back as the Battle of Blenheim 1704, the Battle of Quatre Bras 1815 and there were several recorded (and probably many unrecorded) incidents during WW1.