Just fyi, "yiffing" is a (rather weird) slang term that litteraly means "to have sex." It's only as specific as that. So, sure, "to have sex" is a perverted fantasy, but not really a unique one :/
I think the technical definition of 'yiffing' is actually 'Sex between two socially maladjusted and/or fat people who like to pretend they are animals'.
Ok, you got me there
