The act of looking at something as you drive by. People do it when they come past an accident. Also tourists do it when they are observing the scenery when they are driving. It quite often causes traffic to slow down because the person looking generally slows down a bit to look out their window or windshield.

when all of the sudden traffic gets really heavy and there is no reason for there to be so much traffic until you move up enough to see an accident. all the cars are slowing down and rubber necking to see the car accident which causes another accident and more rubbernecking and so on.

turning and looking a hot woman walk by when you are with you girlfriend

After the act of Anal penetration with a prophylactic, you remove the Condom and slap it against the back on the neck of your partner heightening the pleasure.

After the act of Anal penetration with a Condom, You remove the Condom and slap it against the back on the neck of your partner heightening the pleasure.

A bloke who stands at a bar and loses control over the motor functions in his neck as birds walk past, hence the term 'rubber'necking.