Acouple of weeks ago we were in JFK, they had the congo line going. We called sched and informed them that we would not be taking an extension and that the line was over 2 1/2hrs and that we would time out, they said give it a shot. Well, as soon as we pulled on the taxi way we told the pax that the flight would not go but DELTA has said we have to stay in line and give it a shot. After 2 1/2 hrs we were #5, called sched and said were going back to the gate, they said hold so we went back to the gate, they finally came off hold and informed us ."we just talked to dispatch they can get u off #1", we said pax are already deplaning. The whole time in line we kept informing the pax that the flight would not go and that this was a DELTA decision not ours. Most of the pax were actually in good spirit about it by the end. Delta has become the worse in customer service these days