Ong's disease takes on an added significance if the suffer then contracts a real illness such as a virus or an allergic reaction. The sufferer will be ridiculed by others who will say, for example, "you've got Ong" whilst pointing at the sufferer's affliction.
Ong's/ Ong Disease was dreamt up by a group of young adults after they moved into a house share only to find that their neighbour was a slightly loopy, grubby, annoying lady who would constantly pop around to the house to level accusations of one sort or another. The woman in question was known as Mrs Ong and after one of her visits to the group's home one of the house mates broke out into a severe rash lasting for days, one of the house mates suggested her friend had caught "Ong's disease" from the lady next door.
You might catch Ong's if you go in there.
The man contracted Ong's disease after visiting the ladies grubby little house.