1. This is technically and actually against AAs rules on 'hidden city' or 'throw away' ticketing. Simply you are not using B-C

2. Booking through a travel agent can give you some protection. It will certainly prevent the AA reservations engine from finding duplicates. (IME they find duplicates, but not 'illogical' flights. So 2 departures from SFO, yes...but SFO-DFW-IAD and DFW-JFK that overlap, no.)

3. An agent can cancel the B-C segment so AA isnt seeing you as a missing passenger. The coupon just sits in the ticket unused.

4. Do it once you can probably get away with it. "Well I was going to C, but plans changed so I just booked to D". I've been EXP for about 14 years, spent 70k last year on airfare w AA. and have had it happen a handful of times. Never a comment.