1)
What is "Shechar"?
1.
Sifri (Bamidbar 23 DH mi'Yayin): It is another expression of wine.
2.
R. Eliezer ha'Kapar (Sifri Bamidbar 23 DH mi'Yayin): It is pure wine; Yayin is wine mixed with water.
3.
Targum Onkelos (Bamidbar 6:3): It is old wine.
4.
Shabbos (139b): It is beer made from dates or barley.
2)
What does the verse teach about the songs of those who drink Shechar?
1.
Rashi: They are about me. ("Vi" refers also to this.) Radak - to mock and disgrace me.