I actually experienced breaking a toilet lid by sitting on it once (I’m like 70 kg). It wasn’t even one of those crappy ones. The problem was that it was designed with a slight upward arch and far too few points of contact with the seat, so if you sat down in just the right way (and happened to have your wallet in your back pocket) all the force was concentrated in the perfect way to make it crack.

I used to sit down on toilet lids without batting an eye, but now I am scarred.