#5: I'm a Star Wars.
The young girls of Springfield finally have a fictional Princess Penelope to idolize in Krusty the Clown show. Naturally during a report about inspirational women, princesses are the top picks. Guess who Ralph Wiggum has chosen?
#4: I finished before we came in.
Ralph Wiggum has the unavoidable nature's call during a school trip.
#3: My cat's breath smells like cat food.
This line is one of the earliest catchphrase by our little oddball. It has been recently referenced in season 21's To Surveil With Love.
#2: Even I knew that.
Ralph Wiggum is sometimes smarter than his dad, even if the former is, you know, a special kid. With Homer having failed to pay for information about Lisa, the hired detective framed them up. Consequently Chief Clancy Wiggum has to arrest them with his son Ralph as "undercover police".
#1: Me Fail English? That's Unpossible!
In the episode Lisa on Ice, grades of most students at the Springfield Elementary are at an all-time low and Ralph is no exception. With the news of failing English, he expresses what I consider the best line Ralph Wiggum is known for, "Me fail English? That's unpossible!"