My story is very long and complicated and full of conspiracy theories as to what happened so I'm just going to keep it simple and just ask, how can a second time flyer get "red flagged" at the airport at the very front desk even before going through security?
It is unclear what you mean with ‘red flagged’.
You seem to assume this is a standard term, but it is not - unless you mean an umpire literally throwing a red flag at your feet.
If you mean getting an ‘SSSSS’ written on your boarding pass - it is mostly random selections. I got two of them in about 300 flights over the last ten years - it doesn’t mean anything.