לע"נ מרת חנה בת ר' יצחק יונה
The gemara [Shabbos 139b] tells us that after Yosef separated from his brothers he never drank alcohol again until they came to the palace and וישתו וישכרו עמו - they drank and got drunk together.
I understand why Yosef drank - he knew that he had been reunited with his brothers. But why did his brothers drink? What was their great simcha? They didn't yet know that it was Yosef!
There is a certain type of person who just LIGHTS UP any room he enters. He is the "life of the party". He puts a smile on everyone's face. THAT is [part of] who Yosef was. When he was happy - it was contagious and therefore his brothers caught the fever and became especially joyous themselves. [עי' בס' בת עין במאמרים על שבועות]
That explains the question Yosef asked the Sar Hamshkim and Sar Ha-ofim in jail - מדוע פניכם רעים היום? Why are you looking so sad TODAY?
Why are we sad? Because we are in a miserable dungeon!
And what does he mean when he said "today". EVERY DAY they should look and feel miserable.
The answer is that everyone around Yosef was happy. The air was electrified. So on a regular day they were happy. On that particular day they were crestfallen due to their dreams but normally they were in a good mood.
May we all have a "Yosef effect" on our surroundings.
