I can't possibly drive it AND watch for flex!
I wouldn't be surprised if it does flex some, but I haven't had any loose screws (there, anyway) or problems for the couple of times I've put the flag on.
EDIT: I attached the flag to the bracket and wiggled it good for a short bit (it's cold, dangit). Yep, it flexes where the bracket comes away from the truck and at the other bend as well. The body where it is attached does not visually appear to be flexing but I would assume something is happening there too. All 4 screws are tight and clearance between it and the tailgate has not noticeably changed. Most of it does seem to be in the bends of the bracket that are free of the body. When driving it I tethered the flag to the rack as well, to chill out the flex so it wouldn't keep beating on the truck....that would also mean less flex at the bracket.