I wouldn't say never, but you need to let them initiate it and it needs to be obvious. I've had them bust my chops before - some are funny people, and others are looking to seeing if you're too tense or acting odd.
I've noticed lately that there are now TSA agents in the security lines which are ostensibly there to help direct people, but you can tell they are very high social aptitude people and very smooth. They are feeling people out and seeing if anyone is super nervous or suspicious.
I noticed this before they instituted the "random arrow iPad." I'm not sure about their level of social aptitude though. I got sent to the quick screening line 5 or 6 times in a row, but the people I saw flagged for the slower screening were people who I thought looked calm but less whitebread than me. People with their hair dyed blue, holes in the knees, etc.
I think the person who is actually reading people is the person who checks your ID and boarding pass. Though honestly I think that process would be pretty easy to fool either way.