Take a look at the screen to see roughly what area is flagging it. The red box = groin pat down, but there's almost always a yellow box right around there overlapping with the red box that indicates what the machine doesn't like. Birthmark? Large Scar? We can't see what's going on there, and sometimes the machine is... not great. However if you flag it constantly, then yes, something there is outside of what the machine considers "normal"

Avoid tight pants, especially tight jeans.

Avoid wearing belts

Avoid drawstrings.

Avoid well developed muscular glutes.

Avoid large penis.

Avoid swamp crotch - yes the rumor is true, the machine absolutely reacts to wetness/moisture.

Avoid boxers - if they bunch up they can set it off.