I was involved in a huge charity garage sale on the weekend. I'm a longtime volunteer for the charity, one of the main core of people they can always count on.
Because I'm trustworthy and because my body is happier sitting than standing and/or bending, I'm usually the one who runs the cash box at the garage sale. Not only that, but in this case I brought the table and the chair to sit at. (Previous years we could sometimes find a donated table and/or chair but this year I wanted to be comfy so I brought my own chair and table.)
Before the sale started on Saturday (too early!), I hadn't sat down yet because there were no customers. We were frantically unpacking boxes of donations and arranging them. As customers started trickling in, I decided it was time to get the cash box and set up as "cashier".
Another volunteer (who I hadn't seen before) was sitting at the table in my chair. At one point in my life I might have been too shy to say anything, but after years of reading eHell I'm much more assertive.
I said "Excuse me, I need to sit there and run the cash box now."
Volunteer: "Oh. Well, the volunteer coordinator said that she'd have a chair available for me to sit in because of my back."
I said "Maybe she did, she should be arriving later and you can discuss that with her. I
chair and I'm doing cash now."
Thank you all for showing me how to be more assertive!