Honesty may be the best policy, but if someone has to tell you they're being upright and forthright they're being when talking to you, then it doesn't say much about what they've said at other times in the past.

In this episode of Rule Breaker Investing podcast, Motley Fool co-founder David Gardner explains why his experience shows there is reason to doubt someone's veracity if they find it necessary to call out how truthful they're being. It may be a funny colloquialism, but it still has meaning.

A transcript follows the video.

This podcast was recorded on July 20, 2016.

David Gardner: No. 6. So this one comes out in various phrases, and it always makes me chuckle a little bit. Let's go with the phrase, "I'll be honest with you." There are other variations of this, like "honestly," or "frankly," although maybe those aren't quite as good. Let's just go right to the phrase, "I'll be honest with you."

Have you ever had a conversation with a friend or acquaintance, or maybe somebody who's not so friendly, and that person says, "I'll be honest with you." And right there, right then, in my movie -- in the cinema of my life -- everything slows down, and dramatic music plays.

Because this person is being honest with me at this moment. The humor -- because ultimately, the cinema of my life (and I hope yours, too) is a comedy -- the humor going on here is, doesn't it beg the question, "Are you not always being honest with me?" So anytime I hear somebody saying, "I'll be honest with you" -- honestly, it, by definition to me, calls into question everything else they're ever saying to me, and I'm wondering, "Are you being honest with me now?"