Sorry, this is trivial, but..
There used to be a TV programme (think it was an OU one) and the opening sequence is a man opening the door for a woman, as she goes past him he turns and letches after her bum.
And why do you think that's wrong? (Assuming no-one sees him look.)
I can see it's uncomfortable being admired by people you are not interested in, but it's unreasonable to think their obligation to make you comfortable should extend further than successfully concealing their admiration.
It's not actually wrong for random men to want to take all your clothes off and have sex with you in the office corridor, that's just a normal sex drive at work. Where culture/indoctrination comes into it is that we expect them to conceal that desire. (There's also a health and safety issue, other people trying to traverse the corridor might trip over you both.)
If your lecher were seen, even by a third party, I would agree that he had failed in his social duty.
That is the only reason he opened the door.
How do you know? One can be both polite and lecherous.
As far as I've noticed, most men and women behave identically when it comes to holding doors. If the person you are holding for is worthy of bum-gazing, that is a bonus, not the primary purpose.