When you cross a street with lots of incoming traffic, you will walk parallel to the flow of traffic and in a direction opposite to it. Then, when you see an opening, you will turn and dash through the other side anticipating (hopefully) the incoming vehichles. Seen from above, your trajectory takes the shape of the letter J, hence the expression "Jay walking."
You are walking arcross the middle of the steet with two cops and you go hey you pigs are jay walking and they turn and shoot me a dirty look. And i say relax it was just a joke dummies.
v. To make a pass at a girl you know your buddy has an interest in. Essentially, a G-rated version of "cock-blocking" that can be used with equal effect in more polite company.
Dude #1: "Hey, I totally scored digits from that chick Suzy that always hangs out at Hoffer's".
Dude #2: "Wait, what? You knew I totally dug that chick. I'm calling a jay-walking infraction.
The act of crossing the street because someone before you has already crossed and caused traffic to stop. In effect, jay walking because someone else already has.