One mirror is not enough to see yourself as others see you. When you look at a bathroom mirror you see an image of yourself with left and right reversed. If you don't believe it, extend your right hand to shake hands with yourself. The "person" in the mirror extends his or her left hand.
A bathroom mirror switches left and right in any image it reflects. To see yourself as others do, you need a second mirror to undo the effect of the first mirror and switch the directions back again.
A Complete Reflection
Hold two hand mirrors in front of you with their edges touching and a right angle between them like the two covers of a book when you're reading. With a little adjustment you can get a complete reflection of your face as others see it.
Wink with your right eye. The person in the mirror winks his or her right eye. This may seem strange after a lifetime of looking at bathroom mirrors.
When you look at two mirrors held at right angles like covers of an open book, you see left and right restored to their original relationship. The reason is that the image you see has been reflected twice before reaching you.
When you look at the right-hand mirror you see a reflection of the left-hand mirror, which in turn gives a reflection of the left-hand side of your face. And vice-versa. Two reflections are involved.
This might sound complicated when you're reading it or listening to it, but it's easy to see when you try it.
Martin Gardner, Entertaining Science Experiments with Everyday Objects (Dover reprint, 1981).