Loki had been disappointed with a lot of things that had happened in his life.
He had been lied to for centuries. His father wasn't really his father, his mother wasn't really his mother, his brother wasn't really his brother, and his lovers weren't really his lovers. Grown with, played with, fought with, and laid with – so many things he had done, all with those who had despised his very being. Disappointing.
He had been a peace offering. Nothing more, nothing less. It wasn't fair. He hadn't asked to be saved, he hadn't asked to be raised as a prince, and he hadn't asked to be lied to and pushed into the shadows for what seemed like coincidence. He had lost himself and went mad in rage, anger, self pity. Disappointing.
He had tried to fix it, to make it better. Destroy the Jotunns, save Asgard, prove his worth. Force his "father" into seeing that he could be just as good as Thor, that he could be a king, that he could do it. However, he couldn't. In the end, the idea of him ever being worthy in Asgard's eyes was more farfetched than anything. Disappointing.
He had been saved by Thor and Odin. Without them, his fall into the abyss created by the destruction of the Bifrost surely would have been deadly. He might have been grateful, maybe for a moment, but he would never admit it to himself. Even now, inches away from his death, he wasn't good enough for them. So, he let go – he was a disappointment. Disappointing.
Despite all of that, everything that had happened, everything that he had been through, there was one thing more disappointing than anything. Waking up – alive.