I did explain that books are made in factories, travel in shipping containers, get unloaded by some Saturday kid who's probably been to the loo and not washed his hands, then picked his nose... not to mentioned fondled by shoppers, scanned by the shop assistant etc.
Apparently that is fine, library germs are not. Interestingly the friend in question would happily read library books elsewhere in the home... just not in bed. I wish we had a 'mind-boggled' emoticon.