Another week’s Czenglish mistake, another funny moment for the English teacher!
The word backside – especially in Britain – is a synonym for the part of your body that is just below your back. Your bottom, or er, bum. So if you refer to other things as having a backside, it sounds like you are talking about that particular body part!
In the example, ‘The backside of the building is ugly’, it sounds like the building has a bum! So instead, what you should you say is simply – The back of the building is ugly.
The same goes, for example, for the back of the book. We say – the back of the book, not the backside of the book!