A similar thing happened to me. They asked be to swear to tell the truth "so help me god". I said I agreed with all that was said except that last part. The proceeding continued... (But I sure do find it offensive to have that as standard language in a non-sectarian courtroom).

Good for you! I'd do the same thing if ever asked to swear on a bible, though likely not with the same words you used.

I often accompany my wedding couples to their marriage license appointments where they are asked to hold up their right hand and swear the information they've provided is true. No bible invoked - it could be that I live in a very diverse state, a melting pot of lots of cultures, and/or that the agents know that I provide a secular style ceremony. In any case, I always smile when I don't hear the "so help you God" tacked on at the end of the oath. They are swearing on their own honor, as it should be!