When you maintain eye contact with a stranger, in an oddly sexual manner, perhaps at the grocery store or driving down the street... for more than five seconds, you have successfully managed to "do" someone, eye-sex style.
Be careful though, don't want to share sloppy seconds with your friends ;) SAFE SEX, wear some SUNGLASSES!
(IN THE CAR driving with her girl friend)
Natalie: "OMG, OMG... I just DID him"
Natalie: "That guy over there on the motorcycle... you know, eye sex"
Kerry: "Here's some glasses you NASTY! (throws sunglasses)... don't wanna go catchin' any pink eye!... GROSS"