An insult meaning:
A-Someone's head is big and ugly.
B-Similar to poohead but fatness instead of poo; basically a more convenient way of saying 'fatnesshead'
OW THAT HURT!
Don't tough me again with that thumbtack you ugly fathead!
Person 1: Yo bro, is that a card?
Person 2: Yeah man! It's free cash!
P1: How? Let me see that.. this is a credit card, you owe them money.
P2: I bought 50 MacBooks though.. I thought it was free money P1: No you fucking fathead.