A fork of Rural Dictionary
a common Japanese euphemism for sex (more specifically scandalous or homosexual in nature), this usage was popularized when young female pop star Tomoko Tanabe was shown in a magazine smoking a cigarette, with the caption translating to "Having a smoke in bed together after a friendly meow-meow". It was most likely captioned this way to tiptoe around saying 'sex'.
"Just got back from my girlfriend's's house! We finally got to nyan-nyan, it was so hot."