Until I just goodle'd it now, I always thought there was a rule that TSA agents had to change their gloves, when asked to do so.
I always opt out of the scanners and thus get the groping. If I don't see the TSA agent put on a new pair of gloves, I ask them to do so, and I've never had one refuse, or cop a bad attitude. Most of the time, this is at my home airport and some of the TSA agents there have come to know me and expect it. I had one agent tell me that they are not required to change gloves but they do so when asked by passengers. I just ask nicely.
Out of the country........completely different. I've had some rude agents.
I usually opt for the scanner where ever possible. For me it's faster than the body search since I have artificial hips. Some times the manual body search can take quite a while, especially when the line is backed up, and all that time, your belongings are sitting on the conveyor belt for every anybody to walk off with..... For me at least, the body scanner speeds up the process.
I too opt for the scanner since it is usually quicker, however, I had a disc in my neck replaced with a titanium artificial disc and everytime I come out of the scanner they always have to pat my neck down - kind of weird since my neck is showing and I obviously do not have a bomb taped to my neck!