This quote reflects Holden’s struggle with saying the truth. His admission of being a “terrific liar” highlights his desire for genuineness and his coping mechanism to navigate a society he finds phony.
“I’m the most terrific liar you ever saw in your life. It’s awful. If I’m on my way to the store to buy a magazine, even, and somebody asks me where I’m going, I’m liable to say I’m going to the opera. It’s terrible.”
Holden’s tendency to lie serves him as a sort of defense mechanism, he uses it many times throughout the book and is very good at doing so.