Quote from Ross in The One with the Morning After
Ross: But see, I happen to have a girlfriend. Isaac: Right. That Rachel chick from the coffee place. Ross: That's the one. Listen, I don't want to hurt her. Isaac: Oh, I know. It doesn't matter how much we love them. Monogamy is too cruel a rule. Ross: Listen, can you keep this information to yourself? Isaac: No problem. We gotta look out for each other. We're the same, you and me. Ross: Actually, no, we're not. Isaac: Yeah, we are. Ross: No, we're not. Isaac: Yeah, we are. Ross: No, we're not. Isaac: Okay, we're not. Ross: Right. Isaac: But we are. Ross: Fine. I just need to know that you're not going to tell your sister.