2,733. "I Won't Eat Your Chulin"

Hilchos Nedarim 1:18

If one person tells another, “Whatever I eat of yours won’t be like secular food,” “won’t be kosher” or “won’t be ritually clean,” it’s the same as if he said, “Whatever I eat of yours will be like an offering,” i.e., prohibited. Similarly, if he says, “Whatever I eat of yours will be impure,” “nosar” or piggul” (all referring to disqualified offerings), it is prohibited.

Hilchos Nedarim 1:19

If one person tells another, “I won’t eat secular food of yours,” it’s the same as if he said, “What I will eat of yours won’t be like secular food; it’ll be like an offering.” Similarly, if he says, “The offering if I eat of yours,” “An offering if I eat of yours,” or “Like an offering if I eat of yours,” it is prohibited. However, if he says, “The offering I won’t eat of yours,” “Like an offering, I won’t eat of yours,” “For an offering, I won’t eat of yours,” “An offering, I won’t eat of yours” or “Not an offering, I won’t eat of yours” – in all of these cases, it is permitted because these expressions only suggest that he’s taking an oath by an offering not to eat from the other person’s property, and an oath made on an offering isn’t effective. He might also be understood to be making a vow not to eat an offering with that other person.