"THERE! ARE! FOUR! LIGHTS!"
Who said it: Captain Picard
This line comes from the two-part Next Generation episode "Chain of Command," in which Picard was brutally tortured by the Cardassians. Attempting to break Picard, the Cardassians' interrogator shined four lights in the captain's face and demanded he say there were five—but Picard refused and was punished for it.
When he was finally freed, Picard shouted at the interrogator, "THERE! ARE! FOUR! LIGHTS!" as a way of letting him know that his mind game hadn't worked.