Diamond in the rough

[Vania]

a person who is kinder and more pleasant than they seem to be from their appearance and manner

[Greta]

Someone (or something) that has hidden exceptional characteristics and/or future potential, but currently lacks the final touches that would make them (or it) truly stand out from the crowd.

The phrase is metaphorical and relates to the fact that naturally occurring diamonds are quite ordinary at first glance, and that their [true beauty] as [jewels] is only realized through the cutting and [polishing] process.

[Magaret]

1. A good [athlete] that was either undrafted or chosen late in the [draft]
2. Someone good at something that hangs out with [bad people] who are bad at it

[Dianne]

A sexual act involving a married woman inserting [a diamond] [ring in] [the ass].

[Oralee]

The person that is the [equivalent] to [a diamond] in the middle of all [the bad] things.

[Dave Paprocki]

A girl/guy who is [fine as hell], but lives [in the ghetto] or has [ghetto tendencies] due in part because they lived and were raised in the ghetto.