This so called "Perfect Evening" was so disappointing, as well as discouraging us from coming to your Circle Theatre again.

so 在这里是副词，表示"如此、这样"的程度。 called 是动词 call 的过去分词形式，call 的意思是"称呼、叫作"。 so called 是一个固定短语，意思是"所谓的"，通常带有怀疑或讽刺的意味，暗示名不副实。