Here's something I'm considering: Using lots of alternative names for various religious holidays, like how I always say "Decemberween" instead of you-know-what. That particular practice of mine started when I got a big chunk of the Religious Wrong burning it down because they can't stand the idea of anyone saying "Happy Holidays."
But I digress. I suggest we put together a list of all the religious holidays we can think of, and come up with silly sacrilegious counterparts. Let's not limit ourselves to one religion. Frequency of use will rise when someone gets chauvinistic about a particular holiday.
Here's a bit to get it started:
Easter -> Ovipositional Bunny Day
Okay, so I'm not all that inspired at the moment. I'll get the juices going eventually.