Many, many years ago, I used to flat share with 3 other people. One of the girls was a PITA and used to help herself to my Friday night take out leftovers. So many times I told her not to - but her excuse was “she couldn’t afford nice food and couldn’t afford to go shopping because she’d had to pay the rent that week”!!
After about 3/4 months, I’d really had enough and laced my favourite takeout leftovers with laxatives...she never did it again.
I also used to work with someone who would go through peoples lunchboxes / bags in the shared kitchen, to pick out the bits that he liked. One of my colleagues cottoned on to the fact that he loved prawns. So she made up a big prawn filled sandwich, with prawns that had been left out to warm up considerably...it didn’t stop him!! He had serious food poisoning, but still continued to steal food / cans of fizzy.
My mil....at our wedding, we had bottles of wine / champagne on ice on every table. She took every single bottle of wine from the top table (10 in total) and put them under the table by her feet. Took us ages to work out where they’d gone...she also took the bottom layer of our wedding cake home “to freeze”. We never saw that again, despite repeated requests to have it back. She also left us to pay for her hotel bill from the night of the wedding....