Fascinating episode of a Japanese TV program called Detective Knight Scoop (Tantei Knight Scoop):
A viewer writes in to the program and says that in the village in Miyazaki prefecture where she lives, people spontaneously exclaim "wi!" if they are unexpectedly splashed with water. She also relates that she has heard that people in a particular place in Nagasaki prefecture exclaim "api!" when unexpectedly splashed with water. The viewer is skeptical that people in that Nagasaki village actually say "api!", since "wi!" seems to be the natural, right thing to say in such a circumstance.
The hosts of the show are curious and decide to send out their investigator to check out what the real situation is on the ground. So he takes a road trip from Miyazaki on the east coast to Nagasaki on the west coast, a total of 410 km distance. On the way, he stops off at other places to see what the local people exclaim when unexpectedly splashed with water. The results are nothing short of amazing (and lots of fun!).
The investigator finds that the people of each village he stops at have a different spontaneous exclamation to express their feeling when they are unexpectedly splashed with water. Moreover, they all think that what they say is the natural exclamation that just "pops out" and expresses perfectly their feeling at that instant. In addition, they all aver that this is something they have been saying since the time when they were in kindergarten or other very young age.
A stop in Kumamoto prefecture yields some even more finely grained detail. The general exclamation for being unexpectedly splashed by water is "echa!". To express the same emotion with greater intensity, one would say "echa-su!". If the water is hot, one says "accha!". If the water is hot and your response is stronger than usual, you would say "accha-su!".
At Saga they say "arittsu!". When asked what the meaning of "arittsu!", one very tall fellow from Saga said that it means "arittsu!".
The individuals interviewed believed that, not only was what they said natural, it was also "standard". The locals thought that people elsewhere throughout the nation would all say the same thing.
The investigator did determine that the people in the particular Nagasaki prefecture village did in fact say "api" (or more accurately "appi!") when unexpectedly splashed with water. Further investigation, however, revealed that other nearby villages in Nagasaki didn't say "ap[p]i", but something else, and this was confirmed by one of the hosts (a woman) who came from another village in Nagasaki, and she stated that the people in her village did indeed use another exclamation when unexpectedly splashed with water.
The episode is only 13:24 and the subtitles are adequate for understanding what is going on. I watched the entire episode twice with rapt attention. If you're interested in dialectology, especially field investigations comparing comparable expressions in different locations, I recommend it highly.
All of the places visited are within Kyushu province, while the hosts, most of whom are from provinces other than Kyushu, can't offhand think of comparable expressions in their dialects.
[h.t. Tim Clifford]