To look at someone in a vulger & sexual way.
-Guys who use girls for sex (or girls for guys) have 69 eyes.
Taken from the term "69"ing. Rather than just sex (which could involve love in some cases) The 69, being raunch & lustful is made to the term "69 eyes" because people 'look' at someone with the lustful desire with no attachments.
"Don't go out with Jim, he's got 69 EYES ! You'll be heartbroken"