You might have heard of Bill Maher's movie, Religulous, that mocks those who believe in God. The basic message of the movie is that Maher tries to trap people and make them look stupid to prop up his views. He does so in a sarcastic way trying to be funny. But, most of the time, he just comes off as mean. Of course, he doesn't generally get people who can match wits with him - because he doesn't really want a good response to his questions.
Two things to do - pray for him and then respond with truth (in kindness). Here is a good example: