you must intend to offend for it to be assault. if the intent is to determine if they are concealing a weapon, it is not assault. no matter how offended they are.Intent is an essential element of assault.
you are riding the subway and the train makes an unexpected sudden stop. the lady beside you starts to fall and you reach out and grab her in an attempt to keep her from falling. she gets offended for whatever reason. have you committed assault? you touched her intentionally and she was offended....
you are walking down the street and you see someone draw back a fist in order to strike another person, you grab their arm to stop them. have you committed assault? you touched them intentionally and they were offended.
you are a TSA worker and a passenger sets off the metal detector, they refuse to empty their pockets so you pull them aside for a pat down to ensure they are not concealing a weapon.
It all boils down to intent. the intention behind the TSA patdowns are not to offend anyone.