1. Lashings of: a large amount of, used mainly to refer to things like cream, custard etc.
2. Lash: to strike with a whip
3. Lash together: to bind together with ropes etc
4. To get lashed: this is simply to get very drunk/pissed inebriated/sloshed/hammered/legless/rat-arsed /etc. Lash can also be used as a noun meaning alcohol.
As in: 'Hey, do you fancy going out and getting lashed tonight?'
As in: 'Hey, do you fancy going out on the lash tonight?'