Coined in Vancouver WA, it is a local term to indicate and ridicule a person who is bald on top of their head. It is also an alternative to the weak term "skullet." The only notable celebrities to correctly rock the custard are Reggie Bannister, of the Phantasm films, and Hollywood Hulk Hogan. Calling them a custard is a compliment.
That custard better watch his step, or I'll turn his wife and kids into custards too.