Well, mall cop jobs aren't all that exciting and you probably make his day. You never know, he might have been envisioning a twentysomething woman lurking in the men's dressing room!
Don't let one Neandertal get you down. He doesn't speak for the store.
On the rare occasion that I try something on en drab I make it a point to leave my rejects on the rack in the men's dressing room. I think of it as a way to raise TG awareness among the employees.