[Understandably] there seems to be some confusion regarding rules for threads about members. I'm going to suggest a diyyuk, provide some examples, and hopefully the membership will offer feedback so we can collectively try to understand the rules.
I would suggest that there's a difference between addressing a particular member and speaking about, discussing, or speculating about a particular member.
1. Mazal tov Melech on you birthday.
Mazal tov Melech on your engagement to Lauren.
Acceptable: Here you're really addressing the member and wishing a mazal tov even if it's worded as if it's an announcement addressed to the general memberhsip.
Of course, it goes without saying that Melech has either let his birthday be known, or has specifically ok'd the mazal tov announcement.
2. Whatever happened to Melech?
Not acceptable: It's a thread discussing or speculating about a particular member.
Of course, it goes without saying that those who answer with information known from real life [He was just at my house two weeks ago; I was at his wedding; I saw someone in BP who told me...] are also violating board guidelines.
I miss Melech.
Acceptable if he hasn't been posting. Not acceptable if he has been banned and can't respond. Not acceptable if we start discussing Melech.
3. What's the berachah for oat? Or for Melech: How halachah changes
Acceptable: You're addressing a member.
Of course, it goes without saying that if the thread is insulting it violates other rules.
4. What is Melech's occupation/gender/marital status?
Not acceptable: Your speculating about a member if it's information that member has attempted to obscure. Even if the member has volunteered her marital status, "outing" the member or speculating that the member is lying is not acceptable when that's the purpose of the thread.
Of course, it goes without saying that information from real life is against other board guidelines.
5. Melech, this thread/link/scan is for you.
Acceptable: You're addressing the member. Let's say I asked in a thread the origin of a practice. Answering in that thread would be off topic and then the off topic police would get upset. So the member starts another thread and calls my attention to the thread. So too if a member is well known for taking a certain position. A thread title can address a member where the news link or YouTube link or scan is known to be of particular interest to the member.
6. Melech, happy birthday.
Not acceptable if Melech has been banned or for some other reason cannot respond to or have access to the forum in which the thread is posted.
7. Melech is engaged to Lauren! Mazal Tov!
Acceptable.
This is an exception. You are discussing the member and not addressing the member. However, there is no way that thread could have been started without the express permission of the subject of the thread are therefore there is explicit permission to discuss the member.
8. Members who only use term X on h.com: Do they use this term in real life?
Not acceptable.
Of course, the proper forum for such questions is probably the member forum and not bull.
In this case, the thread starter is intending to discuss a certain member, especially when it's only one member who does so routinely. That the thread starter didn't mention the member by name is immaterial when we all know who the thread starter is talking about - the thread starter is discussing a member indirectly.
Such a thread would seem to violate the rule of not starting threads to discuss specific members.
9. Member who use certain terms on h.com: Do they use these terms in real life?
Acceptable.
The thread starter isn't starting a thread to discuss a certain member. Rather, the question is about in general members using terms on h.com they wouldn't in real life. For example, SDJ - many members use that term on h.com and it's legitimate to ask the tzibbur if they do so in real life.
10. What do you think about the practice of doing X?
Acceptable.
It's acceptable even if the opening all but refers to a particular member admitting to doing X in another thread and it's clear as day this is an offshoot of that other discussion. With the caveat that the opening poster is darned careful to discuss the practice, and only the practice, and not the propriety of the member who admitted in the other thread to that practice.
11. Poll: Is Melech correct?
Unacceptable. You're discussing a member, and all the more so if it has to do with something not on the open boards.
However, Is Opinion X expressed by Melech correct? I'd think that would be ok - you're discussing the opinion, not Melech. But again, the opening poster has to be very, very careful not to contribute to crossing the line of discussing the member.
12. Melech's avatars
Acceptable: You're discussing the avatars, not the member. However, again, we have to be very careful about discussing the avatars and not the member, or even the member's taste.
13. Melech, please empty your PM box
acceptable: you're addressing the member, not discussing the member
So too, "Yo, Melech, this one's for you".
14. Melech, I apologize.
acceptable: you're addressing a member, not discussing the member
15. I figured out why Melech's screen name is as it is
not acceptable: starting a thread to discuss a particular member.
Melech: I figured out why your screen name is what it is.
acceptable: addressing a member. with the usual caveats about real life and lashon hara and outing...
but very dangerous, since it opens the door to pretending to address a member even though your real intent is to discuss the member.
16. Members who do X
acceptable: you're not discussing a particular member
ETA:
I just want to emphasize again that all the other rules [lashon hara, insulting, information not from the open boards, a discussion that the member can't respond to...] apply. As well, not mentioning the member by name when it's clear as day to most of the membership who is being discussed is not an excuse.
I also think there's a difference between starting a thread about a member, where the thread is intended to discuss a member, and starting a thread about a group of members in the collective. I also think it's different to discuss a member within a thread.
I also think that when a member starts a thread that is not appropriate [eg. discussing a member], all the members who contribute to the discussion are just as guilty.
I think the membership has a right to privacy and that privacy includes not being the subject of threads discussing them. However, by participating on h.com, one implicitly accepts being addressed.
I did this list really quickly off the top of my head to invite discussion. I doubt many of the examples would hold up to scrutiny and I don't think even I agree with a number of the examples. Don't hold me [or others] to it. Again, the purpose is to invite discussion to help clarify the guidelines, not to propose setting down any guidelines.

If melech is fine with said post, and demonstrates that by responding within a thread, whats the problem?