So you are lapsed, well and thoroughly lapsed. You reject the teachings of the church; you tell people that you think of Jesus as a historical figure who over time was mythologized into a god; you feel horribly hypocritical if you actually attend a mass, let alone take communion. But can you still identify yourself as Catholic? Sure, you are still Catholic. You are just a lapsed Catholic.
The church is still your community, both in a sacred and secular sense (ooh, alliteration!). Technically, once one is baptized into the church, one is always Catholic. You can't be upbaptized. So no matter how lapsed you are, you still hold this connection. You may regard it as a empty ritual yourself, but others do not. This is one of the things about ritual in general. It is made meaningful by the actions and beliefs of the faithful: ritual has meaning because people do it and believe in it. Really. If people believe in baptism, then it has meaning. A good chunk of the church believes in baptism: this meaning still applies to you, since you are still a part of the Catholic community.
Ok, so how exactly are you a part of this community? Besides its sacred aspect, which you have rejected, there is the secular aspect. Catholicism has become more than a religion, you realize. It is, loosely stated, a cultural group; there are smaller cultural factions within it (for instance, I am Irish Catholic and lapsed Catholic--time for a Venn diagram). There are thus cultural characteristics and experiences common to members, by means of which members relate to each other.
For instance, I went to mass every Sunday of my life (minus serious illness) until I rebelled in sixth grade. I went to CCD, then youth group, hanging out every Sunday with the same kids from the same families for years and years. I went to nine and a half years of Catholic school, including Jesuit university. I say things like "sweet mother of god!", fully realizing I am actually (and my phrasing here is key--I instinctively put "actually" as opposed to "technically") asking for the intercession of the Virgin Mary. I harbor enormous cesspools of guilt for ridiculously long periods of time, over incidents long forgotten or even unnoticed in the first place. Although I am (and have LONG been) thoroughly lapsed, I remain thoroughly and involuntarily indoctrinated.
Another example: one day I was taking a walk with my friend Bethany (not Catholic), and we saw a sidewalk chalk drawing of a heart with a bunch of flames coming out of it. Bethany said, "what is that, sex?" or something similar. I, in contrast, said, "what is that, the sacred heart of Jesus?" This is how I think; this is how I am. You are shaped by your environment; most people, were they brought up Catholic, will retain some Catholic elements no matter how lapsed they are.
Then there is the fact that, if you were brought up Catholic, you almost certainly have a Catholic family. Even if you can excise the Catholic portion of your personality, they will still be Catholic. You are a member of your family: to some degree, what applies to your family applies to you. If your family is a part of this culture, you will always have ties to it as well. That is, unless you are planning on robbing a bank, moving to Aruba and changing your name.
And have you ever gone to church after you became lapsed? Have you talked to the people you know, the choir director, your old youth group leader? What do they do if you tell them you are lapsed? I will tell you: nothing. They talk to you like they always have. For example, when I told her I wasn't getting confirmed with the rest of our group, my youth group leader said: "that's great; you really should wait until you feel ready." Doubt is a part of faith: they know this. To church members, doubt does not make you any less Catholic. It may mean you are going through a tough period, but it does not change you. You are still the same person you have always been; unless they are your mom, they don't care what you consider yourself. They just want you to be okay.
There is another thing to consider as well. Do you really want to excise yourself completely from the community? Do you, for example, want your parents to think of your marriage as valid? Do you want to crack jokes about Jesuits and Franciscans, and have your friends laugh because they understand? It is nice to have a culture, even if you disagree with it. And you can be a part of the Catholic culture and still disagree with it; in fact, you already are. Lapsed Catholics are just as much a part of the Catholic culture as non-lapsed. They are a faction within the cultural group, and important to its identity. Imagine the Catholic church without lapsed members, or religious orders, or ritual trappings. Imagine that the Counter-Reformation never happened; imagine that the Spanish Inquisition was a kind and gentle rural movement. It would not be the same church without any of these elements. You are part of the church; you shape it.