re: laxatives. If the thief is an asshole, and someone who steals coworkers lunches is pretty much guaranteed to be an asshole, then it's pretty simple for the thief to press charges.
It's a misdemeanor at the very least, and possibly a felony for food tampering (as well as aggravated assault charges.)
Do you really want to risk that? Not to mention an asshole also suing you in civil court for lost wages after having to go home and being sick for a week? (No, they wouldn't be sick for a week, but they could easily take the week off and claim they were sick. Tell it to the judge that you're sure they were faking it.) Oh, and of course, the suit would include pain and suffering from a week of stomach cramps.
Also, if smoke starts billowing out of a microwave, someone besides the thief is also going to notice, unless the thief is the only person in the room.
The glaring difference, of course, is that in the case you quoted above, the person blatantly served the laxatives to others. In the case of the OP, the food is intended for himself (or his wife). He's not deliberately serving lax-laced food to someone else.