insatiable drinker; someone who keeps drinking
Refers to a person who, once they start drinking, cannot stop and continues for a long time. Often used in a slightly humorous or self-deprecating way.
He's an insatiable drinker; once he starts, he keeps drinking until morning.
上戸 is a suffix meaning 'drinker' or 'person who likes alcohol'. 後引き上戸 is a specific type of drinker who cannot stop once they start.
下戸 means a person who cannot drink alcohol or drinks very little, the opposite of 上戸.
Compound of 後引き (あとひき, 'pulling back' or 'lingering') and 上戸 (じょうご, 'drinker'). The exact historical derivation is uncertain, but it describes someone who lingers over drinks.