It's bribery of a Federal employee.
The passengers and TSA employee had an implicit agreement that money was expected to change hands if the employee was to help the passengers cheat the line (and everyone in it). It doesn't matter if it happened before or after the cheat.
The TSA employee should be prosecuted and fired. Your friends put convenience ahead of ethics. A lot of people do it and it's not right. A lot of the problems in the United States right now is that people feel like they can "cheat the system". It really doesn't matter how small or trivial the "cheat" is, it all adds up. It's low class on the part of your friends, and a Federal crime on the part of the TSA employee. Plain and simple. This is not how most Americans want our Federal government to work. We all have gripes w/ the TSA, but if we make the system a bribable one, that's even worse. I can't believe there are people out there who can justify it - it just goes to show the sleaziness of some. Too bad we can't expel them from the USA for cheating. For everone one of these creeps we expel, we could make available a work visa for an immigrant who will come here, play by the rules (or get expeled), and do jobs we won't. Unfortunately, we're stuck with your ethics-challenged friends.
Earlier this month, I was late for a connection in Miami. The TSA line at CO's concourse is always a mess when I go through there. I got up to the front of the line by showing people my boarding pass and loudly (and somewhat pathetically) saying I'm late and asking their understanding. I had no problem gettting to the front in less than 30 seconds or so. Even the guy just getting to the scanner pushed his bag and tray back so I could cut in front after hearing me coming his way (I hadn't even intended on asking him to cut since he was already there). People will (albeit some grudgingly) let you though if you ask. You don't have to cheat.