Answer:
I'm not man's best friend, I'm their enemy, I can mark your end, yet you do not see me, I am very small, but very tough, If you have me, then you have it rough.
I'm sometimes white and always wrong. I can break a heart and hurt the strong. I can build love or tear it down. I can make a smile or bring a frown.
My first half is normally made of stone, my second is crazy, and I taste sweet when complete.
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.
Though I wander the earth, I am no longer here. I am pale and I chill everyone near. Who am I?
What did the piece of wood say when he saw the screwdriver and screws approaching?