theatre etiquette

Is it me? Or do some people not know how to behave in a theatre? Over the past four months we have seen people heckle the actors, arriving late and talking during a performance. The worst was someone arriving late, walking up to their seats in the front during a performance and then having a heated discussion about someone who was in their seat! Has anyone else found this. We need to respect the rest of the audience so that we all have an enjoyable experience. Angela