Idioms are expressions which have a meaning that

is not obvious from the individual words. Then the

best way to understand an idiom is to see it in context.

A pain in the neck is not so hard to understand because

no pain is agreeable or nice to have or feel,is it ?

http://www.macmillandictionary.com/dictionary/british/pain_1

By the way,have you ever heard ?

 http://www.macmillandictionary.com/dictionary/british/no-pain-no-gain

This phrase is often used by lots of athletes or people

who exercise a lot and keep looking for new records in

competitions or matches. They have a hard discipline so

that they will get what they want despite their sacrifice

and difficult challenges they face to reach their goals.

 http://www.macmillandictionary.com/dictionary/british/sore_1

http://robingreenacupuncture.com/2014/10/09/5-tips-neck-pain/

Sore muscles and painful bodies are part of their

routines,aren't they ? However , when we refer to

someone who keeps talking and disturbing us any

time,the right idiom to use is : "a pain in the neck".

Examples :

Tina and Mary always talk loudly while they are at

the cinema.They are a pain in the neck !

Janet keeps borrowing money from her friends but

she never returns their money at all.Her friends are

tired of her so they say :"Janet is a pain in the neck !

How about these guys at the photo below ? What can

we say about them ? Have you ever had a problem like

this at the cinema ?