In my opinion, you can wear a poncho any time you want.  What you might want to think about is how to wear them and the design/pattern that you select.  While I have seen women wear ponchos at work (particularly when the air-conditioned buildings get just a bit chilly when you are wear a sleeveless blouse or a tank top), I personally think that you should have several ponchos so that what you wear at work is not what you would need to wear when you party in the evening.

Tips on wearing a poncho

• Stick to basic black or blue (without any visible pattern) ponchos for work.  The ideal fabric is silk or cashmere.  Bloomingdales, Nordstrom, BCBG MAXAZRIA, and eLuxury have a few good ones.
• Choose a plain design for evening wear and depending on the temperature you might want to choose cashmere or wool.  Pair it with a high quality bra top or camisole or tank top.
• You can go with a bold pattern for day time.  Most women like to use a tee or a camisole or a tank top but I have seen women use halter tops or bikinis or even bra tops.
• Ponchos can also be used at the beach and let your imagination run wild in that case.  How about crochet poncho pattern for the beach?
• Don't use a poncho to cover up.  I mean if you are just too lazy to get dressed and think that you can hide it with a poncho - well, bad idea.
• If you choose a see-through/sheer poncho, make sure what you wear inside is appropriate for the situation.  For example, if you wear a sheer poncho at work then stick to a proper blouse.  While going out or on the beach, it is important to check your inner wear carefully.
• While you can wear either a skirt or a pair of elegant slacks with a poncho, what is important is color coordination.  It really doesn't matter what you decide to wear but make sure that you coordinate your outfit.  I like two options:  same or similar colors (perfect for evenings) or contrasts (works much better during day time)

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