"Reverse Gate Screening" is when passengers randomly select a dozen TSA employees to be patted down. I actually carry my own mat with feet marks on it. Be sure to thank the TSA for their cooperation when you're done.

No really...

I think that Eyecue is speaking of the bizarre technique of screening passengers after their flight is complete. This occurs when a breach is discovered but the flight has departed... upon arrival at the next airport, passengers must re-clear security, even if they're not actually going to be flying any more that day.