Explain CAP without the usual triangle diagram.
A network partition is not a choice, it is weather. The theorem is about what you do when it arrives: refuse to answer until you can be sure the answer is current, or answer from what you have and accept that it might be stale.
That is the whole content. The triangle misleads because it suggests you pick two out of three at design time, when in reality you pick one of two, and only during a partition.
So what does "AP system" mean in practice?
It means a read can return a value that another node has already overwritten, and the system will reconcile later. Concretely you get to decide the reconciliation rule: last write wins, vector clocks, or application-level merge. The rule is the real design decision, and it is the part that is usually left undocumented until the first incident.