Shitty lager, possibly short for Grolschlager. In my opinion it is any kind of piss lager that you have to buy when the chips are down, i.e. Pabst, Hamms, Natty, Keystone, Milwakee's Best, Icehouse, or any other derivitive that sells for about 25 cents a can. The word is used in the famous debauchery anthem by Ween
"Booze me up and get me high".
"All that schlager at the bar,
Flakes of gold swim in my brain"
Ween fucking rules, Boognish!!!!!!
After betting all his money on the losing cock at the cockfight, Billy could only afford to drink schlager until the end of the month.