'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'?