Cases like this are why I'd prefer the WBI machines had a placard right at their entry with the following:

1. Wide border in international orange.
2. The title WBI MACHINE in all caps and large print.
3. A notice that going through the WBI machine is optional, and the pax may opt out and be subject to an intrusive pat-down.
4. A notice that WBI does NOT detect weapons or explosives, only anomalies, and any anomaly will result in an intrusive pat-down.
5. A list of DO NOT GO THROUGH THIS WBI MACHINE IF YOU: The list would start with "opt out" and "were persuaded in any way to opt back in."

Someone who is good at designing signs please PM me for the rest of my ideas.