That's not in my Bible
Many Christians have not read the Bible; or, if they have, they may not have noticed some of its odder or more abhorrent passages, such as the injunction against wearing clothes of wool and linen (Deuteronomy 22:11 ) or Jephthah's human sacrifice (Judges 11:30-40 ). Such people may express disbelief that such things are in the Bible.
The best way to counter this argument is to show the person the relevant passage. There are several web sites and books that list questionable passages in the Bible.
There are also searchable Bible applications for smartphones, PDAs, and other mobile devices. It can be useful to have one as a reference.