It seems like you are working with an underwear company or photographer. It makes sense to get the cock a bit aroused so it fills out the underwear in a beneficial way and shows the shape that a man will think he wants. Some guys just get aroused easily as well, as some guys who do modeling might also be exhibitionists. If your boss "requires" full hardon, then it is some kind of erotic situation. I did experience a situation years ago, when I was in my twenties, where I was at a sports clothing store trying on swimsuits. The sales guy would be bring me various styles of swimsuits to try on and see how I looked. The swimsuits were mostly tight and I could barely stay keep myself inside them. I started to get aroused and eventually the salesman took out his cock as he told me I looked good in the swimsuits. Was very erotic and wild, since it was in the changing room of a public store.