Yes very "small minded"!! ------ as if
its probably that person then, who doesnt see anything wrong in it - sure hed be the first to complain if someone pinched his lunch..drink etc.
Do as suggested, make up a sandwich, and either use laxatives..or chillis
Id go for laxatives....the chillis may just make him..or her take one bite and then throw it away...The laxatives will probably go unnoticed, and will take effect.
One really extreme measure is to try and set up a concealed webcam, CCTV etc to catch the culprit in the act...there are some horrid clips of people whove done that, and found out exactly what people were doing in the kitchen.