Duralex glass tumblers were widely used in UK Schools, so you could enjoy a glass of warm tap water with your school dinner. At the bottom of the glass could be found the word DURALEX, which is mysterious to a child because it has an "X" in it.
More importantly, there was a number at the bottom of the glass. This number was, quite simply, your age - for that dinner hour anyway.
The higher the number, the better. Being 2 or 3 was shameful, of course. However, being 89 was better than being 21 - a display of respecting your elders that would leave the doddering old cunts proud.