I'm a charter member of the 'involuntary medical opt-out club' - I'm physically unable to assume and hold the position necessary.

Most of the time, when I'm directed to the NoS and I explain that I'm physically unable to assume the necessary stance, the response is "So you're opting out?" or (shouting or talking into some kind of radio (?) device) "Opt-out".

I originally used the words 'opt out' myself, but I found that in some instances, that clearly indicated to the TSO that I was some kind of trouble-maker. It always resulted in a lengthy bag check, as well as a grope. In other instances, it led to a pointless attempt to convince me of the safety of the device - pointless, because I can't assume and hold the position so there's no way to get a clear scan.