The phrase "immortal line" refers to a special and memorable sentence or quote that will be remembered forever because of its importance or impact. Full definition
At times this litany of abuses might bring to mind Thelma Ritter's immortal line from «All About Eve» — «Everything but the bloodhounds snappin» at her rear end!» (latimes.com)
Come on now, can anyone think of another children's animation that contains such immortal lines as «on guard, you cur! (faith.org.uk)
He was enlisted into the Wehrmacht at the outbreak of the Second World War and by 1945 he had been court martialled for sabotage (he was a paratrooper), captured by the Russians and escaped; captured by the Free French and escaped; captured by the Americans and escaped before finally being captured by the British - who greeted him with the immortal line «Hello Fritz, fancy a cup of tea»! (goalkeepersaredifferent.com)