you could pull out one of the hinge pins and tap the center (or single) barrel of the hinge to one side with a hammer and slightly offset that with respect to the upper and lower barrels. This will cause a little more friction on the hinge pin when it is reinstalled and should be enough to hold the door open.

I usually remove a hinge pin and bend the pin slightly with a hammer---which binds the hinge just a little and holds the door open. I have run into doors needing two pins bent to hold the door open.

Thank you for the responses. One question though, doing any one of these fixes, will the door still work properly?

Yes, the door should still operate just fine.

It is probably easier to reinstall the pin if you bend it slightly as suggested by handymac as opposed to offsetting the hinges.

Thanks, I'm going to surprise my hubby that I fixed it. :)

The door closes because the hinges are not true vertical. put a level on the hinge side of the jamb. if the jamb tilts toward the latch side, it can sometimes be helped by instlling 3" long screws into the top hinge and pulling the jamb tighter to the stud. Cheap easy and worth a try. May have to adjust the latch side also to make the door fit right.
If the hinge jamb tilts in or out from the bathroom, you would probably have to remove the casing on at least one side to try to move the jamb and reanchor it to the studs. Probably not worth it. I would probably opt for the temporary fix method of bending hinge pins.