You are expected to pay for your own alcohol.
Rob is spending the night drinking at the bar with some friends.
Rob wants to save money on drinks.
Rob orders only a couple cheaper drinks he can afford and pays for himself.
Rob orders a bunch of drinks and puts it on his friend's tab.
Rob's friend has an enjoyable night out with him, and they end on a high note.
Rob's friend ends up having to pay a lot of extra money.