How do you try on a pair of pants if there's no fitting room?

Around your neck.

Seriously! In almost all grown ups, the size of the neck is half of the size of the waist. So you can simply close the button and see if you can wrap the waist band of the pants around your neck, and if you can't, you can be pretty sure they're too small. If it fits easily, with a little overlap, there's a good chance the pants will fit you (when worn the normal way, haha) as well.

It looks a little silly, but not nearly as silly as buying a pair of pants from the market or a charity shop and then coming home with them to find that you cannot get into them no matter how hard you try.

(I'm getting a bit of déja-lu here... have I posted this before?)