Drinking yourself into a vegetative state where you are unable to hold a conversation or do anything for yourself. Thus you become nothing more then a cabbage.
"Godsall, you were an absolute Cabbage last night"
A person who is fun in group settings, but when you get them on their own they are boring as fuck. Just like cabbage is fine when you eat it with other things, but on it's own has the palatability of slightly chewy balsa wood.
"what do youthink of Alex?" "I don't know man he's a bit of a cabbage"