Iced coffee carried in your coat pocket.....secure lid or no....uh uh!
The real uhoh is on the subway: for the chairs by the door there's this little ledge below seat level... I like resting my coffee there as I laptop, but I realized it was actually being held a centimeter or so above the ledge by the edge of the chair on the lid -- if it fell it would only be a short fall but then it might tip. But ever time I do this, the cup is fine. It is an exceedingly well-designed lid!