Blasphemer!

blas·pheme 

v. blas·phemed, blas·phem·ing, blas·phemes

v.tr.

1. To speak of (God or a sacred entity) in an irreverent, impious manner.

2. To revile; execrate.

3. To leave fellow worshipers for an "early getaway".

4. Harry Papadimitriou.

v.intr.

To speak blasphemy.

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[Middle English blasfemen, from Old French blasfemer, from Late Latin blasphemare, from Greek blasphemein, from blasphemos, evil-speaking, blasphemous; see bha-² in Indo-European roots.]

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blas·phemer -n.