Well..... (1) a woman is more mature than a girl and is more receptive to such things. (2) Don't let them get you out of your element of correctness... example: her: [angrily] "So, you're saying I'm fat?!?" you: "I didn't say that. I would not say such an attacking thing - that would be completely insensitive to your feelings. I'm not attacking you. I'm here with together with you." her: "then... what are you saying? say it again." you: "I said that I'm wondering if there's anything we can do together to keep ourselves in good health. It looks like you've gotten a little bigger recently and I could certainly use some exercise, so maybe we could workout and diet together and get ourselves in better shape." her: "sounds like 'you're fat' to me" you: I don't feel like you're fat. And for a man to ever say that to a woman would be insensitive to her feelings. I'm not trying to attack you. I'm WITH you and I want to be as encouraging and positive as I can." ... Look, I'm not saying that she's gonna be thrilled to hear it. I'm just saying it's not impossible to communicate such things.
You're right, it's not impossible, but expect some harsh consequences from saying something like that... I just can't see someone saying it like that and getting away with it, unless the girl/woman is too sweet.
Actually, what he meant to say was... He cares about you. He wants to be as positive and constructive as possible. He's noticed that you've gotten little bigger and he wants to be as supportive as possible. blah blah blah...
So that only took 5 pages for a simple question about a the ethics of a guy rooming with 2 girls to evolve into juicystream calling Lady_Di fat.