The Torah tells us that Par'oh woke up after a night of dreaming and was disturbed. He could not figure out what his dreams meant. He called in all his best advisors and wise men, yet nobody could solve the problem for him.
I guess word must have gotten out that Par'oh was upset and was looking for an interpretation for some dreams, because all of the sudden the wine steward shows up again. He tells Par'oh that when he was in jail there was a young Jewish slave with him who interpreted the dreams accurately.
Rashi points out that by an evil person, even when is doing something good, it is not completely good. The wine steward did not just say there was someone in prison who interpreted our dreams, rather he said it in a way that was considered shameful and derogatory.
As King David said, "U' Beyad Adam Al Epolah" - let God punish me but do not let me fall to the mercy of man. People can be cruel and mean and ungrateful. Yosef helped this guy out in jail when he was disturbed by his dream. Yosef gave him confidence in his future and satisfaction from the annoyance of not knowing what the dream meant. Not only did he not mention Yosef's name when he got out of jail, but now he has to do it in a way that will make Yosef look bad and incompetent.
This is whom Yosef relied upon to help him get out of jail, which helps us understand why he had to wait 2 extra years, as a lesson who is reliable and who is not.
Stay away from such people.