I read an interesting tidbit of information somewhere: that it wasn't until the World War II and an influx of American soldiers in Europe that oral became a common sexual practice in the UK; earlier it was considered unhygienic. Now, I don't really care much whether it is true in reality, but I want it to be true in the FBAWTFT-verse.

So, while Newt is not a virgin by any margin of the word, no one has ever go down on him because of cultural stigma among the British. He's completely shocked and speechless when proper, put together, and sophisticated Percival gets on his knees to suck Newt off.