I don't really know anything about the lore but I do know some psychology and I am going to have to side against the both of you for that flesh thing. 

I can totally see a guy being born in a cult where he kills all the time, eventually giving himself up to sex and other primal, selfish desires. Think about it. Being forced to become an perfect assassin would be taxing for a youth. A lot of do this or do that. Tyrion would only experience the selfish desires of his master and surrogate father. Meanwhile those desires that Tyrion is fulfilling are killing and essentially "dehumanizing" people by killing them in droves. 

This means Tyrion only knows fulfilling the self and dehumanizing killing. I imagine shortly after being free of his cult, Tyrion would probably discover sex somehow, because it is a psychological instinct of man. That feeling of sex would feel positive, just like how fulfilling his old master's desires provided positive reinforcement. So women just become faceless things to have sex with because it feels good. Given enough time, Tyrion could probably develop a solid foundation for his seduction tactics. 

Edit: But Tyrion would totally be a rapist if a women refused.