Because they don't even know if they believe.
Boss: I don't know. Guy: I'm not coming in this morning!
Cleaver! EDIT: Also Sharp, knew about this one but I like Cleaver better.
Son: Well you know how it is. Things are always marked down after Christmas!
GtOnly if you go aks your mother.
A rebel without a Claus.
None. They don't believe in a higher power.