As a bochur, Rabbi Sholom Blank, approached the Rebbe to receive a bottle of mashke and extended his left hand. A nearby chossid told him to use his right hand instead, but the Rebbe knew better.
Rabbi Sholom Blank, shliach to Miami, Florida, relates:
During my bar mitzva yechidus in 5717 (1967), the Rebbe asked me if I knew how many strings were on my tzitzis. I answered that there are thirty-two strings total. The Rebbe then took out a piece of paper and wrote down the number 32, using the letters lamed and beis, and then explained that this spells lev, meaning “heart,” and gave me a bracha to have a gutte hartz, a vareme hartz, un a Yiddisher hartz (a good heart, a warm heart, and a Jewish heart).
During one farbrengen when I was a bochur at 770, the Rebbe was handing out bottles of mashke, and called out, “Who is going to Montreal?” Since no one answered, I said that I was.
The Rebbe reached out to hand me the bottle, and I stretched my left hand to take it. As I did that, the elder chossid Reb Yisroel Jacobson called out, “Take with your right hand!”
But the Rebbe turned to him and said, “No, he’s left-handed.” The Rebbe knew that I was a lefty and that, for a lefty, the left hand takes the place of the right hand. The Rebbe knew me.
From The Weekly Farbrengen by Merkaz Anash
I had the zechus to go into yechidus in the Rebbe room in 1976,
At the end of the yechidus, the Rebbe would give us a dollar bill.
I, being a lefty, screeched out my left hand.
My father told me to use my right hand. The Rebbe said, he’s a lefty, “ZUL ER NEMEN MIT ZAIN LINKE HANT”
HE SHOULD TAKE WITH HIS LEFT HAND.
Yet there are other Chasidim that the Rebbe gave them with their right hand even though they are lefties..
Why doesn’t say הלוי the Rebbe is very makpid
The Rebbe responded to Rabbi Jacobson regarding Rabbi Blank “he puts tefillen on his right arm”.
This is how Rabbi Blank says the story