If you have an interior door that swings all the way open every time you leave it slightly ajar, knocking you right in the behind, it means that the door isn’t plumb. This happens for a variety of reasons. Maybe the door frame was built crooked or has settled crooked over time. Or maybe the hinges have come loose, making the entire door hang crooked. 

You don’t need to take the door down and disassemble everything to fix it. Instead, try this much simpler fix that you can do yourself.