I'm pretty sure this isn't possible and I'm 100% sure airlines wouldn't like it but still wanted to check if this could work.

Let's say I want to take this trip:

A-B-C-B-D

But this ticket would cost too much if I bought it direct.

So let's say I find a deal and buy two tickets:

Ticket1: A-B-C-B-A (R/T between A and C)
Ticket2: A-B-D (O/W between A and D)

With both Tickets connecting in B (the hub of the airline)

Now I know that you can't skip any legs, so what I would do is:

1. Use 2 seats for myself on A-B from Ticket 1 AND Ticket 2
2. Then use B-C-B from Ticket 1
3. Skip the final B-A segment from Ticket 1
4. Fly B-D from Ticket 2

Doable?