还…呢【hái … ne】

还 + a noun + 呢 mocks someone for falling short of what that label promises. It's spoken, and the next clause usually says how they fell short.

亏 in front makes it sharper: "and you of all people".

还 + verb + 呢

With a verb, the same frame scolds someone for doing something they have no business doing.

Said warmly, it reports something better than you expected, "even".

我还以为…呢

还以为…呢 says what you believed until a moment ago, and that it turned out wrong.

Without 呢

Drop the 呢 and the mockery goes with it. 你还是老师 is a plain statement, "you're still a teacher".

• × 亏你还是老师，怎么能说这种话 → 亏你还是老师呢，怎么能说这种话

还没…呢, "not yet", is a separate pattern; there 呢 just softens the sentence.