1 Corinthians 10:27

If any of them that believe not bid you to a feast, and ye be disposed to go; whatsoever is set before you, eat, asking no question for conscience sake. (KJV)

Then: This is specific advice for a specific situation and the Corinthians understood it as such. They would not generalize the teaching to other times or other circumstances. N. T. Wright points out the principle of not being the source or cause of uneccessary offense (p. 137). If one is invited to eat out, eat what's there.

Now: Christians today cannot follow this advice willy-nilly. By no means do they smoke, take drugs, or indulge in other unseemly conduct just to make "friends" feel good. In doing as asked, believers will denigrate, not glorify the gospel. There is a point at which a conscience cannot be violated. Each individual knows where it is.