A door that refuses to stay open is a truly frustrating bit of household disobedience. Snap that door into shape with a pin bend, and learn a few other door fixes while you're at it.
Now's as good a time as any to look around your house and fix doors that stick, open or close on their own, bend, or otherwise provide an imperfect seal inside a frame. For doors that swing closed or open on their own, Popular Mechanics recommends bending the hinge pin a bit with a hammer (pictured at top-left in our little matrix picture mash-up):
Rather than resetting the hinges or propping it open with a potted plant, remove one of the hinge pins, lay it on a hard surface, and strike it lightly with a hammer until the hinge pin has a slight bend. Tap the pin back in place. The increased friction will keep the door where you want it.
Popular Mechanics has four more fixes at the link, and you're free to tell us what door annoyances you've repaired on your own in the comments.
Door Repair 101: How to Fix a Squeaky Door Hinge, Gaps, and More [Popular Mechanics via Apartment Therapy]