Is it bad form? Yes Tacky? Yeah Is it the end of the world? No.
I wouldn't do it. I wouldn't bring a can of soda or a beer into a restaurant.
Maybe would bring a drink or snack for a child, but not an adult.
IMO, of course.

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I was walking home one night and a guy hammering on a roof called me a paranoid little weirdo. In morse code. -Emo Phillips