Just what the title says "Who do you lust after but shouldn't?"
For me it's probably just about every woman I know that I shouldn't lust after...lol. My step-daughter, my wife's sisters, my brother's wife, many cousins, many of my wife's cousins, pretty much all of my wife's friends, my best friend's wife and his daughter and many more.
I always find ways to let all of these women know that I find them beautiful and sexy and many times it's paid off. I might not have got to actually fuck them but still had fun with them in one way or another.