Wood – Should I keep a bathroom door open or closed to keep it from expanding

Like user2492 says, it's almost certainly moisture. Wood will warp and change shape as moisture levels change, and depending on the grain, each door may warp differently. Unless it's raising the bottom of the door for different flooring, or removing a lot of layers of paint, I leave shaving the door down as a last resort. Prefab doors are all designed with specific clearances and any mistakes are almost always from the installation.

To fix the hinges, you have two options, push things out or pull things in. Since you have to lift the door, you can push it out from the bottom and pull it in at the top. The most frequent issue I see is the door trim pulling away from the building frame at the top from the weight of the door. And the easiest way to pull that in is to remove the highest screw that is also closest to the hinge pin, and replace it with a 3" deck screw (assuming you have wood framing). The deck screw doesn't have threads in the last inch, so it will pull the hinge and door trim towards the framing when you get it all the way in. The reason for replacing the screw closest to the hinge pin is to also get the hinge to twist a bit and close tighter (compare the closed top and bottom hinge when the door is closed to see how the bottom hinge fits tight). Just be careful that you don't over tighten the deck screw and cause cracking or a lot of paint damage on the door trim.

Should you not be able to use a deck screw (e.g. non-wood framing), or for anyone that needs to push the hinge out, you can use a washer behind the hinge and return the screw through that washer. If you put the washer closer to the hinge pin, it will cause the hinge to stay open further when closed. And if you put the washer away from the hinge pin, it will cause the hinge to close tighter.

I am not a contractor, and this is a real do it yourself type approach. This is provided at your own risk, and I assume no liability for damage.

The only thing I can think of that is going to auto reset in the way you've described is a device powered by gravity. Everything else ( anti-kick devices installed backwards, anti slam devices) either won't allow the door to close or need to be manually reset.

I picture a small piece of plate steel rather than wood, for durability, that has a hole bored in it, along the top edge, perhaps in the center, perhaps 1/4" - 1/2".

Through this hole pass a bolt whose body is less than the hole size, but whose head is too large to pass through (you'll likely end up with 1/16" or 1/8" clearance on the inside of the hole, which should be fine. You'd want to use a bolt that is threaded right to the head as opposed to those that are only partly threaded. You might need to scratch your head a little to get the bolt length right, but I'm thinking that a 5" bolt with 1" into the wall might be enough (remember that at the corner of the door the gap will be much more than 4").

You will also require a self locking nut for this bolt, some washers and some sort of threaded hole you can install into your door frame (there are hammer in threads available, just make sure you plan ahead size wise, some people would just hammer in a nut).

To support this contraption, I picture a wire back to the wall, but a firm brace like a piece of rod or wood could also be used. The brace should look like an upside down triangle when it's installed.

Drill a hole in the top of your door frame, within an easy reach of the door handle (you'll need to reach it to get out of the room), and install the threading. Make sure that you leave enough room for the plate to swing upside down and still clear the door.

Place the loop of wire/support rod on the bolt next to the head.

Place a washer on the bolt and pass it through the plate. Place a washer on the bolt (so that the washers are sandwiching the plate) and put the nut onto the bolt, so that the washers and plate are close, but not firm (if it's too firm, it's too hard to swing it out of your way).

If the door blows closed, the nut will prevent the plate from sliding back to the door frame and thus striking your pet.

When you want to open the door, you swing it open (the plate is between the door and the jam).

When you DON'T want the door to close, do nothing, (the plate's in the way) and gravity will reset the material.

When you DO want to close the door, swing the piece of material out of the way and close the door. When you want to get back out, you'll have to push the plate out of the way again, and leave, gravity resets.

Ok so that's really a lot of text, but it's a diy description ...

I personally think it's easier to use an anti-slam device and put it somewhere remarkably annoying so you can't forget it. Something like this, put over your sink faucet while you use the washroom. They come in really big foam finger style designs, that would probably help give your pet time to get out of the way or prevent some injury.