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Would be denying such advertising really be a violation of the first amendment?
Some communities do prohibit the posting of billboards that violate their local decency standards. My hometown, for a while, prohibited a Black Velvet billboard that had a sultry blonde suggestively dressed. But someone sued for the right to put it up, and he (I am assuming) won.
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Is this type of advertising sexual harassment?
In the sense of perpetuating the sexual objectification of women, yes. Could you imagine a Victoria's Secret outdoor advertisement on a road that leads directly into an Amish settlement?
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Could a women claim legitimate suffering and mental anguish?
Possibly, if it was in conjunction with someone saying, "Hey, you look like that model on Victoria's Secret? So what panties are YOU wearing today, hmmmm?"
If it produced undue attention and embarrassment where the woman lives or works, yes.
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Could it be presented as such in a court case?
Yes. But under the circumstance that I mentioned above, the corporation would be a co-defendant, with the person or persons harassing her being the primary defendant(s). But unless the plaintiff could prove that the advertisement actually caused her some form of injury (psychological or physical or affecting her employment or social status), the case would be dismissed.