It can be hard to describe in so many words..and depends on what you mean by "bad" hoof. I've seen some with really pretty hoof walls that had all sorts of thrush/rot problems when you picked it up or had other sole issues. Yet I've seen some horses with lots of grass cracks and chips that overall had really healthy, sound feet.
Bad trims, however, can be spotted. Tall, steep feet that look like the horse is on stilts (usually happens just with shod feet) are lameness cases waiting to happen.
Long toes/low heels where it appears the hoof/pastern angle is broken back is another extreme in the opposite direction.
Deep cracks, missing chunks are indicating the lack of a trim in most cases.
Thin hoof walls that are prone to flaring and splitting are mostly a genetic issue, compounded by bad farrier work or poor nutrition.(TB's are the best known for thin walls)
Horses with thick hoof walls tend to get the bad angles and massive broken chunks eventually , and again, is more of a genetic blessing/curse, depending on how you look at it.
A good, well trimmed hoof, should short, with the hoof wall angle matching the pastern of the horse. The hoof should land heel first or flat when in motion. The horse should stand squarely over it, not appearing to be leaning forward or backward. The hoof itself should be free of cracks/chips/ breaks and especiall flares. Upon picking it up, there should be a smooth, concave sole. The frog should extend about 2/3 of the sole's length, and be firm, and almost "meaty" looking. The bars (extension of the wall that turns and runs parallel to the frog) should taper off into the sole and only extend a short ways along the frog. There should be no foul odors or crumbly, powdery gunk.
First two pics are of the same horse..he had had "stilts" for feet for a while, but this is after a few trims/pulled shoes. He has great, sound feet now. Need to update them. The angle was a little high in the heel, but overall, I think it shows a nice hoof.
The third and fourth pics are two diff. Horses. The third has thrush, broken, weak hoof walls, despite the thickness and was tender footed. The last hoof is one that has thin walls prone to splitting and cracking, obviously the pic is documented before I pulled the shoes. Believe it or not, that shoe had only been on 5 weeks, I think! Just a taste of what bad feet can look like.