Hi Saskia,
I have flown internationally several times as well as domestically in Canada and the USA. In Canada, our security procedures state that you may be asked to undergo a private screening, and I have been subjected to an ignorant and rude male security guard trying to demand I lift my shirt in line in front of everyone to show what's under my shirt. I loudly refused and told him that I would be happy to deal with a private screening with a female security officer, but that I was not required to lift my shirt in public any more than anyone else. I had the private screening and immediately complained to his supervisor, and he was addressed. In my other travels, I have routinely been asked to touch my belt or stomach area and then had my hands tested for explosive residue. This is pretty standard in North America, but I do not have to allow them to do it in line and can ask for a private screening, etc.
Traveling to Cuba, no one cared and no exam.
Traveling to Costa Rica, we had to deplane and go back through security in El Salvador. This created some issues with the language barrier, and I was escorted to a private screening room. They were very good about it and had two female officers with limited English who were very apologetic but had to document the private screening. With some help from Google Translate, we got it sorted. They were overall good about it, just did not run into it often at all.
I have taken to traveling wearing a stealth belt which, for me, makes it easier to do the explosive screening right in line as I am not exposing anything and no one even notices. I would definitely complain to the airport, especially since you travel so often; they need to educate their staff better.
Cheers
Marina