After an incident in Afghanistan, a mission gone wrong, Tyson doesn’t wear anything with too tight of a collar. He was held prisoner for several days during which his air was restricted for most of the time and he passed out because of it more than five times. Sebastian was also part of this mission and suffered similar treatment.The clothes that he wears are either very loose and bellow his collar bones [t-shirts and polos] or stop on the collar bone and are tight enough that they can’t slip any higher [basically anything else other than dress shirts and formal dress shirts*].When he wears a dress shirt he doesn’t do up the top button and lets the tie or bow tie [or any other type of fabric worn around the neck] keep the collar closed. When he wears a formal dress shirt he’ll close the top button but keep the neck wear loose to avoid triggering any flash backs.*Having come from an upper class family Tyson considers anything worn on the torso that isn’t a vest or item of clothing worn over a shirt [blazer, jacket, coat, et cetera] to be a dress shirt. What most people would normally call a dress shirt Tyson calls a formal dress shirt.
This also leads to him having a twitch trigger attack instinct whenever someone touches his throat.
Touching and holding the back of Tyson’s neck is a good way of reassuring Tyson and keeping him calm, like holding a puppy or kitten by their scruff, but any fingers straying past his jugular will lead to an instantaneous attack. Even hands straying too far up his collarbones from touching his shoulder can put Tyson on the defensive.