He could have just written his name on his yogurt.
Roommates sometimes eat each-others food in a shared fridge, which causes tensions if people wanted to keep food for themselves. Writing one's name on food items is a common system roommates use with a shared fridge to make sure people don't eat what they shouldn't. But here, one of the roommates has gone over the top with a new system to prevent people from eating his yogurt: locking up the fridge/kitchen and putting traps everywhere it so it's inaccessible.