My carryon bags get searched 100% of the time and I get searched about 50% of the time. The joys of traveling with medical equipment and supplies, including medical liquids that exceed the 3-1-1 rule. I therefore plan on security taking 30 minutes, not counting the time spent in line. If it takes less I am happy. For me, not a big deal, its the price of flying.
Now, one time, when they swabbed one of my carryon it tripped their explosives test. THAT was an interesting experience. It took more than my planned for 30 minutes at security, more searching and swabbing of bags and me, lots of questions, forms to fill out, and attention from multiple security people, though they were very professional and pleasant about it. I don't know what caused it, however all of my personal care products (shampoo, body wash, hand soap, etc) contain glycerin, so that is a possibility.
I agree with the previous poster... if you are concerned a piece of clothing is going to be an issue, don't wear it at the airport. Pack it or leave it home. When I fly I wear clothes that are comfortable, functional, and safety-minded (sneakers, natural fibres like cotton.... I have been on three planes that have had to do emergency landings and am cognizant of the possibility of needing to quickly evacuate a plane) and part of that is also that make getting through security as easy as possible -- eg no belt, if possible no metal buttons or zipper, layers.