Well known Las Vegas comedian/magician and atheist Penn Jillette is known for being outspoken in his atheism (In January 2007, Jillette took the "Blasphemy Challenge" offered by the Rational Response Squad and publicly denied the existence of a Holy Spirit).
In this video Jillette recounts an encounter with a Christian who gave him a Bible and witnessed to him. Penn waffles a little at the start of the video but watch it through because his comments contain some very revealing (and convicting) information about what many atheists think about "lukewarm" Christianity. Check it out . . .