Replacing an interior door lock, such as the one on your bathroom's door, does not automatically mean calling a locksmith. Replace the door's lock mechanism yourself, saving yourself from having to wait for the locksmith to show up and also saving on the money you would have paid him. You only need a new lock assembly and some basic tools, as well less than half an hour of time.
Look over the base or cylinder portion of the door knob to find a small hole or holes where the knob's retaining screws are located. Use a flashlight if you are having trouble spotting the holes.
Insert the tip of a small flat head screwdriver into the hole and turn the screwdriver counterclockwise a few turns to loosen the retaining screw. Repeat this step for every hole you find.
Grasp the door knob firmly and pull on it, removing it from the rest of the assembly. Use the tip of the screwdriver to remove the smooth plate that sits against the door and slide it completely off the assembly.
Use a Phillips screwdriver to back out the screws that hold the door's lock assembly in place. Slide the lock assembly out of the opening in the door and slide the new lock assembly into place in the same orientation as the old one.
Tighten the screws that hold the new lock assembly into the door, then slide on the decorative plate and the door knob. Tighten the retaining screws for each door knob by turning the screwdriver clockwise.