"SDOO" stands for self-directed (positional) opt out. This refers to the act of positioning oneself nearest the metal detector at an airport security checkpoint so that
one can avoid screening by an AIT
machine (either X-ray body scanner or MMW body scanner). It doesn't always work. There are THREE possible scenarios which can ruin a good attempt at a SDOO: 1)
TSA "smurfs" block the WTMD with some type of object or themselves, 2) a
TSA "moat
dragon" demands you go through the AIT, or 3) both scenarios #1 and #2 occur simultaneously. The term "SDOO" is commonly encountered on frequent flyer forums, such as Flyertalk, where travelers discuss options for avoiding unnecessary radiation exposure or aggressive
pat-downs at security checkpoints.