I don't even know where to start. My home (a log cabin built by the previous owner) is a veritable shop of horrors. Some of the highlights.
1) One day I was leaning into a door by holding on to the piece of trim above the doorway. It came right off in my hand. It wasn't nailed or glued into place, just balanced on the vertical pieces of trim on the sides of the door.
2) The light switch boxes were apparently installed as a result of very little planning. They are too close to the door opening so that a notch is cut out of the trim around the door to accommodate putting the switch plate covers on them.
3) Many of the electrical circuits aren't grounded. It's not that there isn't a ground wire, it just isn't attached to the outlets/switches in the circuit. For some reason they are just cut off as they enter each box.
4) Scariest one - There was an ungrounded and obviously no GFI circuit than ran right next to an above ground pool. If the wall of that pool had leaked or collapsed that would have been an electro-fest.
5) Rigid Satillo tile installed right over the junction of two foundations (that weren't tied together). I'm sure you can guess why I know EXACTLY where those foundations meet.
6) A wire running along the outside of the wall and joined with electrical tape (no box) mid circuit. I didn't notice it until the water heater (right next to this) started leaking right onto that splice. Very scary.
7) The heat pump is installed in a small closet just so that to replace the filter I have to twist it considerably to fit it through the opening, usually mangling it.
8) Tons of trees planted way too close to each other in the yard. Now they are large mature trees that look like they are wrestling.
8) The plumbing in my well-house is unnecessarily haphhazzard. It is a made of stepping over and ducking under pipes just to get to the water softener, which I have to do carrying 40lb bags of salt.
9) The drain for the tub (clawfoot) is set right in the middle of where the tub goes instead of at the end where it belongs. It took some creative plumbing to make that work. The first plumber I called needed to escalate it to a more experienced guy from his company.
10) The electrical line from the main breaker to a workshop in the yard was strung across the yard like a clothesline. Had to be careful not to choke myself on it when mowing.
I've fixed several of these and continue to do so as my budget permits.
I forgot to mention that the previous owner was such a cheapskate he would regularly underpay people who came out to my house to do work or intentionally nitpick their work in an effort to negotiate them down AFTER they finished the job. Several repair guys I've called had to be convinced I there was a new owner before they would come out.