Brewer's Droop refers to the inability to achieve or sustain an erection while drunk, and also to impotence caused by too much drinking over a lifetime. i.e.:

• Johnny goes to a party and pairs off, but he is unable to have sexual intercourse because he is too pissed and can't get it up.
• Johnny hasn't been able to get it up for the last eight months, due to many years of alcohol abuse.

Note that both these instances are labeled 'Brewer's Droop'.

In Australia, Brewer's Droop is sometimes called the Foster's Flop.

The term is used in Blur's 'Parklife' where it refers to a man suffering from the second scenario: "John's got Brewer's Droop, he gets intimidated by the dirty pigeons, they love a bit of it"