This could be the most commonly asked question here on FT. As others have stated, if you miss any segment of your itinerary other than the last, then the rest of your itinerary will be cancelled. If you check bags, it's virtually impossible to do this without an overnight somewhere.

There are also ways that the airline can choose to punish you if they choose to do so, even though I don't think they usually do it unless you make a habit out of it. They could charge your credit card for the price of flying CCC-BBB, which will usually be quite a bit higher than the cost of flying CCC-BBB-AAA. If you're a FF, they could do a few things, up to and including closing out your FF account. Once again, that's not something that they usually do unless you make a habit out of this type of thing, but it is something that could potentially happen.

However, none of this matters as you want to miss the first leg, which will cancel all remaining legs. So that just means you'll have to pay the walk-up fare to purchase a new ticket onto the plane and hope the seat is still available.