Utter disrespect is the number 1 destroying factor regarding happy relationships. So many people who are ensconced in their relationships begin to take each other for granted. They cease to be exciting to each other. They also stop treating each other as special. They start to treat each other in the third person. They cease the art of appreciation, start to take each other for granted, even start to exploit each other because after all, that is what their significant other is there for.
Their disrespect not only applies to their actions but in their speech. They talk to each other in ways that can be classified as verbally abusive. They feel that they can speak to each other that way because they feel that they somehow have ownership over the other partner. They furthermore feel that since they are in a committal relationship, they are comfortable enough to do as they please. In essence, they can really let go and be as tactless as they please.