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.:
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" | 
