Above: From January 7, 2009: Besides the plethora of font types, sizes and colors, the Thai government cabinet website continues to show unusually worded reasons for prime ministers leaving office. I bet you didn’t know Thaksin left office because of the “State Administration Assembly on September 19, 2006” (the date of the coup).
Above: September, 2014: Gen. Prayuth gains office by “General Assembly resolution National.”
According to the website, the last PM specified to have been appointed to office by a coup is Kriangsak Chomanan in 1977. The last PM specified to have left office due to a coup is Chatichai Choonhavan in 1991.