When you are reading a newspaper on a train, sometimes you find the person sitting next to you leaning over your shoulder to see what it is that you are reading. The individual stretches his neck in order to do this. Such a person was called a “rubberneck”.
Nowadays, the word is used to refer to someone who stares at someone or something.
A tourist, since he is always staring at something, is often called a “rubberneck”. The word is mostly used in American English and is considered slang.
*The rubberneck in front of me moved at a very slow pace.
The word can also be used as a verb. When you “rubberneck” at something, you are staring at it. *Stop rubbernecking at the screen. Switch off the TV and finish your homework.