this is said refering to cutting, a technique usually associated with people known as "emo". This phrase is taken from a joke, saying "make it count" "go down the lane, not across the street" Cutting is when one takes a sharp object (razor usually), when depressed, and cuts their wrist one or more times. saying "go down the lane" is cut down the wrist, not across it. cutting down the wrist is dangerous and even life threatening (if you cut an important artery), compared to across the wrist.
please note* emo is not a label, even though this word often used to describe a certain group of people (and this group is known for cutting more than any other group)
Jenny: "i feel so depressed lately"
Jackie: "Your not going to start cutting are you? Because if you do, make it count! go down the lane not across the street!! ahaha"
Jenny: "Your an insensitive bitch and i hate you"