Private dick, though it may sound dirty, or even redundant, it really isn't as bad as it sounds. A 'private dick' is merely a modern term for the classic private eye, which is just another nickname for a private detective. I don't know why private detectives deserve so many nicknames, but it seems that they've gotten this one because of their reputation for being...well...not-nice people. Also, they kinda poke around where they're not supposed to be.

Sounds rather fitting to me.