'Japanese Motorbike', UK slang, east Midlands area. Euphemism for the female ailment also known as 'Thrush'(Medical term. Manifesting as a mild to severe skin itching caused by the opportunistic yeast infection 'Candida Albicans').
Original Example of use: "When she told me she had an 'ItchyFanny' I thought it was a type of Japanese motorbike".
The slang term has evolved in recent years with women using the slang term knowingly.
A woman who warns a prospective partner she "has got Japanese motorbike" is being socially responsible by politely warning of an "itchy fanny" (an intimate medical issue recognised by general medical practitioners as a mild topical groin infection. "Fanny" (noun, coarse UK English slang term for pudenda).
Why are you scratching your twat dearest, have you got 'japanese motorbike'?
Definitions include: It means that the person in question is trying to get the attention of the person they are speaking to, but the person they are speaking to is lost in their own thoughts and not paying attention to them. Because the person is said to be 'spacing out', they are being contacted by earth.