"I believe you were just proven wrong? "
That sentence isn't an interrogative one, it's a statement. Lose the question mark.
"I know only 5 people in my schools theatre department that are not full of themselves."
You were still incorrect. According to your own rule, which can be disputed, if you look it up, you're still incorrect. You should haved spelled out five
Megan Mullally as Karen Walker on Will and Grace: "Tell me more. Tell me more. Like does he have a car?"