Often times a few different rebbes are mentioned (either previous Chabad rebbes or rebbes of other Chasudusim) in the same talk and then the word "The Rebbe" comes in and it's ambiguous.
I have heard the 7th Rebbe called:
I don't really think any of these are adequate.
I've never heard him called:
What's the best way to avoid confusion?
A couple of other possibilities:
"the Lubavitcher Rebbe zt"l (or some other appropriate honorific)" - my preferred form on this site and elsewhere
"the late Lubavitcher Rebbe"
In conversation with non-Lubavitchers, "the Lubavitcher Rebbe" is probably unequivocal enough for most purposes (and in conversation among Lubavitchers, "the Rebbe"). It's much the same with other branches of Chassidus too, I think. If you say "the Bostoner Rebbe zt"l," I think it will generally be understood that you mean the most famous one of the line, R' Levi Yitzchak. Similarly, "the Satmar Rebbe zt"l" without further qualification would probably be taken to mean R' Yoel Moshe.
Supplementing, not supplanting, others' answers: In Hebrew-language Lubavitch publications he's often referred to as אדמו״ר נשיא דורנו or even just נשיא דורנו. (That will, of course, be false in a few years, and I wonder whether it will continue (among those who maintain he's no longer the נשיא).)
He is to be called either one of the two, you can say any of them to anybody in Manhattan and they will know who you speak of:
Rabbi Menachem Mendel Schneersohn
The Lubavitcher Rebbe
Since it is controversial whether to say "shlit"a" or "ziyah", one can simply omit the suffix, thus keeping the peace.
The best thing to call the 7th Lubavitcher Rebbe is R' Menachem Mendel Schneerson, z"l (zichrono l'vracha)
Within Chabad circles, "The Rebbe" is a sufficient designation. In a similar way, everyone knows that in YU circles, any mention of "The Rav" is a reference to R' Yosef Dov Soloveitchik, z"l.
I think that the only confusion that may ever be engendered is over whether you are referring to the Lubavitcher Rebbe or to another rebbe altogether. Nobody is ever going to think that you a referring to a different rebbe of Chabad unless you add some kind of additional descriptor (Rashash, Rashab, etc). When I was in a Chabad yeshiva, a few of us used to refer to the seventh rebbe as the Rebbe mamash. Aside from emphasising that he was really the rebbe, it also singled out who was being referred to by his initials: Menachem Mendel Schneersohn. When I moved on from there to a Litvak yeshiva, I can assure you that nobody misunderstood who I was referring to when I simply mentioned "the Lubavitcher Rebbe".
Good question!
For the several decades that the late Rabbi Menachem Mendel Schneurson zt'l, the 7th Lubavitcher Rebbe, held that title, he was simply "the rebbe"; his deceased father-in-law, Rabbi Yosef Yitzchak Schneurson zt'l, was "der friedeger rebbe" (the previous rebbe).
Had an eighth Lubavitcher Rebbe been named, this would have been much simpler: he would have taken the title "the rebbe", and some other term would have been used for Rabbi Menachem Mendel. (The same last name between the 6th and 7th rebbes makes this all the more confusing.) But there hasn't been a Lubavitcher Rebbe since.
In subjects intended for broader audiences, I'd probably spell it out, as I've done above:
Rabbi Menachem Mendel Schneurson zt'l, the late seventh rebbe of Lubavitch.
Or something like that. But if you need a quick reference in conversation, I don't think we have a good convention like {the rebbe, der friedeger rebbe, the rebbe rashab, der alter rebbe}. "The rebbe menachem mendel" sounds diminutive." "Rabbi Schneurson" is ambiguous.
Does anyone have a better answer for this one?
I think this depends on who is talking. if it's betweens habadniks they could just say our or the rav it would be simple. or if a habadnik is talking to someone else he could say my rav. in any case as you asked I think the best way to avoid confusion is to say which rav rather than say rabi. so I suggest you refer to him as the admor milubavitch. in my experience when people are refering to other than the last one they specify by nicknames.
Just to throw out another possibility: the most recent Lubavitcher Rebbe.
In use: The most recent Lubavitcher Rebbe's middle name was Mendel.
"The Rebbe" is sufficient. We all know who we are talking about by now when this is said. People sometimes purposely pretend this is ambiguous for whatever personal reason but we all know who we are talking about. The Rebbe is not only the Rebbe for his chassidim but for all yidden. Even other chassidic Rebbes went to him for brochos and advice (btw there are video recordings of this happening)
