Lots of good advice here. I can't believe that someone would care about what's essentially an undergarment. If you somehow end up on the losing side of this situation and still want to keep your job, I would suggest looking at some kevlar t-shirts. While they won't provide nearly as much protection as an actual ballistic or stab vest, they will protect against most knife slashes. You'll be out of luck against firearms, but it sounds like knives are your main concern anyway. I have one and they are no thicker than a regular shirt and certainly won't be noticed even if someone touches you.