I think you can say either. I think poor and bad can be used interchangeably in this instance. I'm interested to see what others say though... I could be completely wrong. Wouldn't be the first time!
This is one question I did not know the answer to! I looked it up, but can't find any answer. In every example I found via google, they were used interchangeably. Personally, I agree with NC -- I'd use poor. But I would love to know the real answer if anyone has one!
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"We live in an age where unnecessary things are our only necessities." --Oscar Wilde
Yeah, it came up in Spanish class today (oddly enough, not English) and I said that I'd always thought it was supposed to be poor grammar. Everyone else seemed to think bad grammar was okay, I guess because it's more commonly used. It just sounds funny to me to say "bad grammar" but I didn't necessarily know if it was wrong.
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Bad taste is like a nice dash of paprika. We all could use more of it. It's no taste I'm against. -Diana Vreeland