Referring to hundred dollar bills -- Benjamins or benjamins?

I think I would capitalize it.

I also think "Benjamin Franklins" sounds better.

I'm not sure what the rap artists/teens/drug dealers prefer.

Diddy capitalized it.

The Urban Dictionary says it's 'Benjamins.'

Ya mean C-notes? Benjies? Sniffers? Binary bills?

This is one of those things that the copyeditor will put in your style sheet. Whenever you use a word NOT IN WEBSTER'S, he/she will put a question mark the first you use it, and then list it in the style sheet in order to be sure it's used the same every time.