You so cranky about gay folks' annexation of the word "gay"! Uh, sir.

(Seriously, this is not a new observation, but I'm always amused by how much linguistic sympathy of this sort "gay" gets. Makes you wonder where the champions are for all the other words which have changed or expanded in meaning since the 17th century.)

The word he gives for "switch", dondengaeshi, apparently derives from kabuki stagecraft also known as gandougaeshi (龕灯返し or 強盗返し), where -- if I understand correctly -- the set would be rolled over backwards 90 degrees, such that the current background would pass out of view and the next background would roll up from the floor and become visible.

The gaeshi part of the name means "turn" or "reverse" or "switch around", and the gandou part is apparently related to a type of flashlight/lamp known as a gandoujouchin (龕灯提灯 or 強盗提灯 -- 龕灯 or 龕燈 were the original kanji, while 強盗, "robbery", were apparently ateji applied because the device was often used by robbers). As for the mimetic name, the drums would go don-den-don-den while the change was happening, is the word on the street. And so, in any case, the word came to mean sudden and dramatic change, and specialised from there.