NOW it's a "non-uniform, UNIFORM", i.e., EVERYONE has pressed "casual" FBI tan-chinos, pressed polo shirt, unscuffed docksiders, mirrored sun-glasses, wastebag that screams "SIDEARM..!".
Oh, and a Motorola radio printing through front right pants pocket.
Right?
A Hawaiian shirt is ideal undercover wear:
Baggy allows belt carry.
Bold pattern breaks up any outlines.
Makes you look like a dopey tourist.
But realistically, the best way to blend in on most flights is to dress like an absolute slob.