I hate seeing people with dirty necks

[MikeBrownsJob]

If youre talking about necks looking like that pic above, that is not there because of dirt.

That's excessive sugar/diabetic type shh right there.

 

[MikeBrownsJob]

http://en.wikipedia.org/wiki/Acanthosis_nigricans

 

[Heafcliffe]

 

[Takerstani]

Its usually an indicator of diabetes or the onset of it. I forgot the exact term.

I was coming in to say this. It's not always dirt. Sometimes it's for this reason or even other health/skin issues.