A play on the phrase, "You want fries with that?". It is a reference to a girl that is as easy to get as fastfood with as many diseases as fastfood has too. The cream in the phrase refers to cream that is used to get rid of STDs.
Tim: I think I'm going to ask Julie on a date man.
Old Greg: You want cream with that?
Old Greg: Do you want cream for all the STDs she's going to give you?
Tim: What are you talking about?
Old Greg: Dude, Julie is a mad hoe.
Tim: Fuck that's shitty, but thanks for warning me bro.