Can I tell my friend she has big boobs?
What makes you want to remark on your friend's large breasts?
I think they are awesome and she is hot.
Just because you are sexually attracted to your friend, that doesn't make it right to treat her like an object of desire. Be respectful of your friend and keep your sexual observations to yourself.
Why is it so bad? I am just looking out for my friend and trying to help her out.
How do you think your friend will respond when you tell her? Don't you think she might be offended? Do you really want to risk your friendship?