I actually agree that it's annoying as well. It's not pretentious.... you are PAYING for that service. That's what First Class is all about and why the prices (or the frequent flying you did to earn those seats) is so high. Just like people who can pay for a suite at Four Seasons or can hire a private chef in their home... the more money you have, the more you get exclusive to you. Doesn't matter if you are a businessman, or you look like a scrub, or you're 7 years old. Welcome to America.
I know some people look at First Class and think "well it's an empty bathroom so I'll use it" and I don't blame them. But really the flight attendants should be saying "these people paid for this bathroom, you paid for the one in the back. use the one in the back, sorry."
It's the FA's fault for not enforcing the rules.
E