The standard head shakes of disapproval. Comments like "she should just go through the scanner like everyone else" or "look at her trying to create a problem".
After the first couple walked by and had such a reaction, I just ignored it. But then when it repeatedly happened, I wondered why so many people were bothered enough by her decision that they have to stop and make a snarky comment about it.
It could also be out of guilt. It is much more uncomfortable to see someone doing the right thing, when you know that you have chosen the wrong, and easier path. So you have to rationalize it verbally somehow.
