C.M.
My daughter has a habit of saying things like that. When she says it, I say "What makes you say that?" and then I listen. Usually it's a sign of frustration and an inability to make things they want them to be.
Usually by calmly talking it out, my daughter is able to see how silly she is being and also able to get out her frustration. I will often say "Okay, what do you want to do about it?" For example:
"Everyone hates me!"
"What makes you say that?"
"Everyone is ignoring me!"
"Why do you think everyone is ignoring you?"
"Well, I want to play Wii, but no one wants to play Wii with me."
"Okay, what do you want to do about that?"
"I want them to play Wii!"
"I understand. Is there a way you can compromise?"
"They want to play Hide and Seek."
"Can you suggest that you all play Hide and Seek and then play Wii?"
"Okay."
Offering solutions just makes the child feel like you don't understand or are belittling his/her frustration. By talking it out and having them come up with their OWN solutions they will learn how to solve these issues for themselves.