Click here to read all about it. With alcohol keeping ADH from doing its job, you produce a lot more water-diluted urine, which fills the bladder quickly and makes you have to pee more often. Ya wanna come round? So you go.
It could either be used specifically, "Are we gunna get on the piss? He's piss fit all right! If someone has a good tolerance to alcohol, or if they are used to consuming it, then they are said to be piss fit. Additionally, alcoholic beverages can be a bladder irritant for many people and the carbonation of drinks like beer and champagne can cause gas and pressure that contribute to that irritation.