Any TSA employee using his status as a federal employee (doesn't have to be in uniform) for personal gain is guilty of a government ethics violation. I've posted on this subject at length a couple of times before. One of the rules states that a government employee may not use his/her office for personal gain. Jumping ahead in a coffee line, extorting free food & drink, or entering an airline club without being a member are all examples of this rule. If a coffee shop employee offers free coffee or some other perk, the TSA employee may not accept it.
I would be interested in feedback from some of the TSA employees who post here concerning the mandatory ethics training they receive (initial and recurring), particularly if this type of violation is addressed and enforced.
If you see this happen, report the individual using the DHS IG hotline. (Search on me and I have posted the particulars many times.) If you have the time & the intestinal fortitude, confront the screening clerk directly and/or go back to the checkpoint and talk to the supervisor. At the end of the conversation, inform them you are going to report this to the IG.
FYI, the government does not make a distinction between a "small or harmless" ethics violation and a "big" one. It either is or isn't.
Here is the source material: U.S. Office of Government Ethics
Ethical conduct of government officials (I am one.) is a HUGE hot button with me, if you haven't already figured that out.