I can't seem to remember this particular word/phrase. I'm almost certain it's a two-word phrase. It specifically refers to someone who is skilled with the ladies, ie, someone who knows the tricks of the trade.

Usage:  

- "Unless you're a X-Y, that's not going to work with her."

Edit : 
I'm not looking for 'ladies man', 'casanova', 'womanizer' etc.
This phrase refers to someone who's more of a pro and one who is serious about his business.