ratbastid

I'm of the opinion that while sexual proclivities and interests MIGHT be explainable, they don't NEED to be explained, and they "why" of why the person is interested in that is probably best left unquestioned. The embarrassment of going into "why you like that weird thing you like" is basically guaranteed to drive the person attempting to broach the subject back into their closet.

You like what you like. Some desires are common and some desires are unusual. That's really all there is to it.

You don't have to choose to indulge him, but if you do, I'd recommend you do some googling on scat play. Presumably there are safety precautions you'd want to study up on.