1.Someone who worries entirely too much.
2. A name for someone who always worries about everything, and is in danger of growing warts from it.
Based on the old saying that if you worry too much you will grow warts.
A Worry Wart "I don't know guys, I don't think we should go to Burger King, I've heard bad things about that place."
Someone Else "Shut the fuck up and stop being such a worry wart.