Maybe I've been lucky, but I seem to run into more decent screeners than the contrary. I will admit that the few bad apples do tend to stand out in memory more.

Its the system thats the problem, IMO, and not the front line screeners.

An example: I was passing through IAH and I had forgotten a brand new bottle of cologne (about $70 USD) that I hadnt even opened. Of course I got popped by the x-ray guy for a bag search and the lady searching my bag was very pleasant. She was obviously very sympathetic about the situation (this was genuine). She tried to make it fit into a mailbox slot so I could mail it home, offered to help me through the line if I wanted to go back out and check it, asked if there was anyone I could call to pick it up, etc. Clearly a decent human being just doing her job enforcing a ridiculous rule. This is the way I see the majority of TSA screeners.

Now if I would have started insulting her, barking, asking for supervisors, threatening her with [fill retalitory action here], etc ..... I can't say that I can predict what would have happened. My best guess is that either:

1) I would be lucky enough to be confronting a screener with excellent self control and I would have simply left looking like an a**, or
2) I would be unlucky enough to be confronting a screener who would equal or exceed my level of unpleasantness resulting in all sorts of unecessary stuff.

my 2 cents (keep the change) :-)