Most Hunter ceiling fans. Seems most all their models today use the dinky rubber inserts on the mtg plate. They tear off too easily. The fans usually hang crooked and need a lot of balancing. Any ceiling damage around box further complicates the process.
Ceiling medallions, especially the oval shaped foam or plaster type 2 or 3 inches thick. Gotta have a spotter on the floor to keep it straight, use x long screws up through to the box, sometimes the bracket or dome doesn't fit properly. The proper glue can be hard to find and gluing is messy. Then another mess if customer wants to remove it later. Some of the large plastic type medallions are ok.
Chandoliers with independent support wires & brackets, especially if in combo with ceiling medallions.
Wiremold if it has to be bent much at all. Great for a straight run on a flat wall. Hard to make decent looking bends and the paint scratches easily.
Hockey pucks with screws the size of splinters or shavings. Try buying a box of these screws, IF anyone carries or can order them.
Flourescent lights with emergency ballasts. Troublesome, ballasts are high dollar. Multiple feeds needed. Much better to have frog eyes on the wall nearby.
Generators with both standard and metric hardware. Generac use to be bad for that, plus they had some odd sizes not included in all wrench/socket sets.