You should never touch your eye but with your elbow.

The saying uses an absurd condition—reaching an eye with an elbow—to insist that one should not touch or rub the eyes. Its force lies in making the prohibited action practically impossible, rather than merely advising caution.

It may also suggest extreme restraint around something delicate and easily harmed, though that broader application is interpretive. Most directly, the image warns against casual contact with the eyes: when an action risks damage, keep one's hands away.

Use it humorously or emphatically to tell someone not to rub, poke, or otherwise meddle with their eyes. It may be extended playfully to a particularly sensitive matter, but that use goes beyond the wording’s direct eye-safety warning.