I have never had a problem anywhere in Iowa, Missouri, Minnesota, or the other states (Indiana, Kentucky, Tennessee) I traveled through last summer on a trip with my kids. I have chosen not to wear one on two occasions. Both were concerts in very large venues, with security details at all the entrances. I don't think it would have caused a problem there, either, because frankly the security folk were not all that observant. Still it seemed smarter to just not go there.

As for the definition of "dagger" or "dirk" it is left intentionally vague by the legislators, and the officer on the scene (or the prosecutor) have wide discretion.