I used to fly all the time, and I can say that on average, the TSA agents I've encountered have seemed like decent people doing a job....However...

...I have also run into many instances where one or more complete #$%!'n jackasses has been harassing someone, or trying to harass me, for no real apparent reason. It's possible that some may just be riled up from some earlier confrontation and don't quite understand the concept of professional demeanor, but generally speaking, it usually boils down to a combination of ignorance and what is most likely some psychological defect.

This is where having some extra time, staying calm, and knowing the law and your rights (at least to some minimal degree) can be enormously helpful. I've personnally had TSA attempt to pull a variety of crap on me, including the ol' grope routine (never sucessfully), but have on more than one occasion been able to watch their stupid dejected faces when the supervisor instructed them (after a calm discussion) to let me walk through the standard metal detector unmolested.