worked with a chap once,we played a practical joke on him.
Start a day before chatting about crocodiles living in the sewers, say you saw it in the Daily Mail.
Next day continue the converation, and say you googled it and that there are dwarf ones living in the house sewers as large ones cant get round the bend in the bog.
Later that afternoon, put a plastic crocodile down the bog, with its mouth open, and tomatoe sause on its lips, now close the lid, and stick down with some Blu tack, get the victim to lift the lid, after saying the lid had stuck and the toilet was making funny noises.
Stand well back as the victim lifts the lid, as he will fly out screaming like a queen.
Or my victim did.