To get (very) drunk
Also 'to go on the lash'.
Synonymous with:
Get pissed, get
wasted, get hammered, get rat-arsed, get
sloshed, get trolleyed etc
The word 'lash' orinally means to
strike with a whip, and so has this extended meaning (ie. drinking makes you feel like you've been flogged).
NB. Usually used in a positive sense.
1. "Hey
John, what are you up to tonight? The
boys are all going out and getting
lashed"
2. "The boys are all going out on the lash tonight."