Where can guys get lessons in being a gentleman?

i just read a question posted by an anonymous asking for advice on why he made a girl at work uncomfortable. I’ve been wondering for a long time

why do some (very few, by the way) guys understand being a gentleman and are respectful and manly while others seem completely lost? where do men learn manners and how to treat a woman or at the very least, self-respect in when faced with a woman he disagrees with
Where can guys get lessons in being a gentleman?
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