In AKC breed standards, what does 'reversal of sex characteristics' mean exactly?

Not sure about the context (maybe a quote would help?), but if it's the context I think it is (i.e. such a thing is a fault), it refers to the size, mass of head, bone, etc.

i.e. You don't want a b itchy looking, refined dog, or a blocky, heavy, doggy b itch.

I assume this would mean what we (in my breed at least) refer to as either a "doggie bit ch", or a "bit chy dog".

Each sex should look a certain way. Size is a factor, but in my breed, the bone mass and head mass are bigger in dogs. A bit ch that has too much bone or too much head would be a "doggie bit ch".

A "bit chy dog" is a male that lacks those things and would look more like a female. LESS desirable than the "doggie bit ch".

It means that dogs (males) should look "masculine" and b tches(females) should appear feminine.

It means that you should be able to tell just from looking at a specimen whether it's a dog or a b tch...

This refers to height at the withers, substance, weight, type of head(as in muzzle)....

Here is part of the Rottweiler standard:

General Appearance

The ideal Rottweiler is a medium large, robust and powerful dog, black with clearly defined rust markings. His compact and substantial build denotes great strength, agility and endurance. Dogs are characteristically more massive throughout with larger frame and heavier bone than b tches. B tches are distinctly feminine, but without weakness of substance or structure.

Size, Proportion, Substance

Dogs--24 inches to 27 inches. Btches--22 inches to 25 inches, with preferred size being mid-range of each sex. Correct proportion is of primary importance, as long as size is within the standard's range.

The length of body, from prosternum to the rearmost projection of the rump, is slightly longer than the height of the dog at the withers, the most desirable proportion of the height to length being 9 to 10. The Rottweiler is neither coarse nor shelly. Depth of chest is approximately fifty percent (50%) of the height of the dog. His bone and muscle mass must be sufficient to balance his frame, giving a compact and very powerful appearance.

Serious Faults--Lack of proportion, undersized, oversized, reversal of sex characteristics (btchy dogs, doggy btches).

Well I've never seen it worded that way in any standard but in most breeds males are bigger and coarse than females and females are smaller and more refined. This would be referring to a small refined male (also known as b*tchie dog ) or a large coarse female (also known as a doggie b*itch).