Getting in the piss

One of the highest ranks of expressing how intoxicated you are, or will be. More aggressive form of 'getting on the piss' or 'OTP', as you are quantifying how deep you will be getting in the piss, rather than just getting on it. (See also: piss = alcohol/alcoholic beverage).

John: What are ya up to tonight mate?
Darryl: Getting in the piss bro.
John: How deep?
Darryl: Till I can't feel my legs