A gas-guzzler is a car — sometimes another vehicle — that uses a huge amount of petrol. The phrase is informal and mostly American: gas there means gasoline, and to guzzle is to drink in greedy gulps, so the car is pictured as gulping fuel. People say it with a mix of joke and complaint, about old thirsty engines, big SUVs, or anything whose fuel bill hurts. Though actually, school English in Taiwan often teaches petrol, not gas, for 汽油; the set phrase still says gas because it was born in the United States. It names the vehicle, not the driver.