Is masturbation a sin in Vajrayana variety practiced in Bhutan as official state religion? When performed by non-monk, for example, adolescent boy, divorced man, as part of wider sexual practices used by partners, etc.
Masturbation is not a Dharma practice, even in Secret Mantra.
It is not a sin for laymen. Even for monks, it will become a "sin", if it's goal or end result is ejaculation, but not otherwise.
I get the impression that the word 'sin' is wrong when applied by a westerner toward Buddhism. The concept of sin is in and of itself a western concept and as such does not directly apply. The 'sin' is relative and depends on context and is therefore diffused by virtue of relativity and context: and we see that the sin is in the eye of the beholder and not defined a priori as SIN. The concept of God does not exist in Buddhism. Sin is not really sin at all but mearly an opportunity to experience a path which may provide an excuse to change for the 'better'?.