When someone is talking, it's rude to interrupt. If you'd like to share your thoughts with the person speaking, wait until they're finished, then wait for the appropriate time and place to make your thoughts known. This goes for presidential addresses in Congress, award-winner speeches, and everyday folks like us just trying to share stories with each other. Being courteous of others isn't difficult. Respect is something everyone deserves, whether or not you agree with the person who has the floor. You are entitled to your own opinion, but that doesn't mean you should steal someone else's spotlight just because you think your opinion is better.
*Stepping down from soap box*