Good Riddles

Question: I am a big threat to humanity,
but you wouldn't get rid of me even if you could.

What am I?

Question: What do these things all have in common: Laughter, living well, and a good offense?

Question: 4 people fall out of a boat and only 3 get their hair wet.

Question: When the clock has no angle I will own yesterday, tomorrow and tonight What m I?

Question: Two men are facing each other alone in a large room. There is a clock on the wall. One man, who thinks of himself as a prophet, says to the other, "In five minutes you'll be stabbed in the back."

The other man is very distraught and stares at the clock. After five minutes he is stabbed in the back.

What happened?