"Turning Japanese" is a song by The Vapors released in 1980. It is a love song. However, many people believe it is about masturbation.

Though I cannot vouch for the credibility of the website on which I found the interview with the song's author, I can see no reason to doubt it:

Over in the States, "Turning Japanese" was deciphered as a paen to masturbation - more specifically the Oriental-looking facial distortions one pulls in the moment of climax (so I'm reliably informed). Fenton is characteristically reticent on such matters. "It means whatever you want it to mean," he says, before admitting: "I wrote it as a love song. But when I went to America everyone said to me, "Is it about wanking?" In interviews, I'd say alternatively, "Yes it is", and "No, it's not". It could be about a lot of things. I just woke up with that phrase in my head. It's just an image which captures what that song was all about. But, no it wasn't intended to be about wanking at the time. What surprised me was that the Americans thought it was an English phrase!"
Source: http://hem.passagen.se/pareng/vapors.htm, click "The Story." Feb. 9, 2003

So, according to the interview, it could be about masturbation, but originally, it was written as a love song.