Most Helpful Opinion
Having just left a job in menswear, I feel compelled to comment.
First of all, in reference to the second link, don't...ever...wear pants like that. E...ver!
Secondly, when wearing a casual shirt like that, you should only unbutton the top button. Depending on the shirt, the environment, the event, etc., you could get away with doing the top two buttons, but I usually only do the top.