Armor...
Good question!
I'm not aware (for whatever that's worth) of any law against it, so long as you're not engaging in various high end felonies, however, I've been reading that the FBI has a policy that interprets the wearing of body armor as "just cause" to suspect something illegal is going on, and therefore they can detain you, search you, torture your poodle, etc etc etc.
I dunno. It's a tough call. Armor is tough to explain if it's discovered, not that it should be.
Mine's got a metal trauma plate in it, and I damn near walked through a metal detector with it once. Ended up having to do a discrete U turn, and drop the plate off in my car.