A 74-year-old woman in Idaho was caught vandalizing library books by pouring condiments into the book drop.

Boise police were on the lookout for over a year for someone who had been pouring various sauces on more than 100 of the local library’s books. They finally managed to ‘ketchup’ to the culprit in May 2010, and it was one of the least likely people imaginable - a little old lady! 74-year-old Joy L. Cassidy’s in a real ‘pickle’ now - the officers had been staking out the facility and caught her pouring an entire jar of mayo into the book return! Cassidy could be linked to ten other similar ‘hot dogging’ incidents over the previous year, which means she may be responsible for thousands of dollars of damage! She indicated some sort of a motive to the police, but they have not released this information - perhaps she just ‘relished’ destroying public property?
(source)