I would like to second my agreement with what
@DREW WILEY and
@Vaughn have said. I think it is too common for oafish comments to get lightly dismissed as, "boys will be boys," which may be true enough, but none the less, likely to sound offensive to some forum members.
One litmus test participants might use before posting a comment about female anatomy would be to ask themselves, "Would I say this at the dinner table if my mother, wife, and daughter were present?"
To my ear, the comment, "I've seen better knockers," does not sound like part of an inherently respectful exchange of views on a public forum, and probably should have been self-censored.