DS1 used to call it "beest" as in "breast." My husband found that very embarrassing... Now he's almost 2 and he's switched over mostly to "nuhse." While it's less explicit than "beest," it also comes along with a lot more commentary -- instead of "wan' beest" it's "I want to nuhse. Amma, I want to nuhse now. Nuhse in two-bed (my bed.) Nuhse in two-bed now. Nuhse that one. I want to nuhse that one in two-bed now!" So there's much more time for someone to pick up on what he's talking about.
DH is mostly on board with the nursing thing, but I think he's starting to think enough is enough. DS isn't two yet, but he looks like your average three-year-old.