[Penny]

I did that once, I ran up and down the aisles in the supermarkets screaming at the top of my voice and Mum was only one aisle over...

Then there was the time I set the burgler alarm off at work and everyone thought it was the fire alarm, and were all outside waiting (including myself) until they realised it was the burgler alarm.

And the only other thing I can think of (cos i told someone else this story recently) was having to explain to a work mate what Wanking was after using the term, as english is their second language and he wasn't familar with the term...