I saw this on Twitter a few weeks ago, via @amyalkon, and I’m so going to use when people claim that atheism is just another religion:
“If atheism is a religion then not collecting stamps is a hobby.”
Other variations might work too:
… then watching daytime soaps from your parents’ couch is a career.
… then starvation is just a different kind of eating.
… then not giving to charity is a way of being charitable.
I still prefer the “not collecting stamps” version, however. Any others?