Think this is a good idea. If several people use the same refrigerator, not clear how the OP is certain it is one specific person. If you see someone not close it, that would be a great time to tell them. Communal refrigs are always an issue at our office, so most either bring a cooler/insulated bag or lunches that don't require refrigeration. Would hate to see what the refrig looks like at the home of several of these people LOL.