First, fill something to the nick of overfilling. It just doesn't matter what it is: a bag almost bulging with stuff; a cliff in its weight limit; an almost full elevator; a morbidly obese gourmand's stuffed stomach; you name it. When you've finished, add just a teeny, tiny bit more. Watch your recipient blow/crack/shatter instantly and/or loudly. This trope applies to situations where maximal capacity is reached, and even an infinitesimal quantity surpassing it causes effects far more massive than common sense could predict. Examples of Wafer-Thin Mint include: