Is it Kind? Is it Necessary? Does it Improve Upon the Silence?
We're all about supporting our fellow songwriters and want you to do the same by offering comments that help them, not hurt them.
So don't be a jerk. It's not reasonable for you to like everyone's song, so if a song doesn't speak to you, just move along. There's no reason to say 'wow, that song sucks' because a comment like that doesn't add anything to the conversation.
Choose words that help the songwriter grow. Remember this is a painful and deeply personal experience for many of us.