There's a bit from Heinlein's Podkayne of Mars that's been relevant lately.
Girdie smiled her sweet and secret smile that always means she is thinking about something she doesn't intend to be fully frank about. Then she said, "Poddy, girls are taught to be 'insulted' at such offers for their own protection-and it is a good idea, quite as good an idea as keeping a fire extinguisher handy even though you don't expect a fire. But you are right; it is not an insult, it is never an insult-it is the one utterly honest tribute to a woman's charm and femininity that a man can offer her. The rest of what they tell us is mostly polite lies ... but on this one subject a man is nakedly honest. I don't see any reason ever to be insulted if a man is polite and gallant about it."
Even when I was young and read the book for the first time, this advice seemed dubious. Assuming, for the sake of argument, the gender roles in the quotation... I don't see a proposition as necessarily indicating anything more than that the guy has decided that she's of a sex that he likes, meets his minimum standards of hygiene, and has one or more orifices that he thinks would be fun to play with.
Taking another look at it, I don't understand the comparison to a fire extinguisher and an unexpected fire. The all-too-rare occasions when a woman might be propositioned? The extremely unlikely possibility that the guy might not be sincere in his intentions? The vanishingly-unlikely possibility that the guy might be too sincere in his interest, i.e. an obsessive stalker?
See also: Elise Matthesen's post on
how to report sexual harassment.