This question , according to some users, makes no sense. It is about the possible origin of the metaphorical usage of the term "beak" to refer to a "man mouth". Please help me understand what sense is missing and in what way it is off-topic here. The origin of terms and their usage may require considerable research and a clear, precise answer is not always possible. It that the problem with my question?
I'm very new here so I'm probably off-tune with the general mood or tone, but from my current perspective - as I commented there - your question makes perfect sense. Whether it is a good fit for this site is more difficult for me to tell as I'm new, although it looks to me that it fits well, but regardless I think you might be taking too seriously the "goliard / frat-boy" (not in a particularly good taste IMO and probably not appropriate for this site but still not that serious) attitude that user @ElberichSchneider showed. Hopefully he can clarify how your question makes no sense but if I were you I would not feel the need to follow-up too much on this.
I've seen many questions of yours asking for the origin of a term / idiom.
While it's my personal opinion (and apparently also some other users') that often terms / idioms stem from themselves, this has nothing to do with the legitimateness of such questions (which by the way I personally find useful and interesting).
And technically speaking, I can't see a reason why those should be off-topic.
We have an etymology tag on purpose.