To drink huge amounts of beer or lager simply to get very, very drunk. Not to savor the taste or flavor, but just to get wasted. The phrase is used in London and parts of England, usually associated with wide-boy or East-end types, although a trip to Ibiza might be rewarded with a few examples too.
"C'mon boys! Let's get lagered-up! Look at the locals, they're waiting for us to get proper pissed! C'mon boys! Lagered-up! Lagered-up! Waaay!"
by Liquid Sky September 15, 2009