The crucial background information is that my mother keeps a box full of greeting cards in her desk at all times. Wedding, anniversary, get well, birthdays for both children and adults...you name it. She will never be caught unawares without a greeting card handy.
I don't remember how this all started, or more importantly, why. I was about four years old. One evening I was sitting at her desk coloring or something while she was ironing in the same room. I got the idea that wouldn't it just be the funniest thing ever if I took one of the cards and put a silly word in it and gave it to her. So I picked this valentine with a bear on it and the word came to me. This was going to be the BEST.
"Mom", I asked, "how do you spell 'toilet'?"
"T", she began patiently, "O I L E T", she slowly continued as I, being a four-year-old with limited writing experience tried to keep up with her and mind my penmanship at once, followed her instructions with the utmost concentration. She asked why I wanted to know how to spell "toilet" and I'd smirk and say it was nothing. Then maybe seven minutes later, I told her I had a surprise for her, give her the card, she'd open it, read my clever message, give me that "oh, Megan" mom-look and I collapsed in giggles.
Oh, but I didn't do it only once. Every couple of weeks or so, I'd think to myself, ya know, that card gag would be a good one right about now, and get the card back from the box that I had carefully erased "toilet" from last time and have to ask her how to spell it again. And she'd ask why again. And I laughed just as hard every time she opened up her valentine and BLAMMO! TOILET!