I had to steal my own bike, too. My sister and I met in our cars at the appointed location then rode together on a local "Rails to Trails" route. We stopped for lunch and I locked our bikes together and also to a timber column to the deck of the restaurant. Upon finishing lunch, I found that I didn't have the key to the Arbus heavy duty chain lock. The key was in my car located thirteen miles away. I had my car key with me, but not the key to the bike lock.
First part of this fail: Not keeping the key with me.
Second part of this fail: Not keeping the bike lock locked. If the lock was locked before I could use it, well, I wouldn't have been able to use it since I didn't have a key with me. Then, I would have never found myself in this situation.
Luckily, there was an outdoor sporting goods place nearby. They sell and rent bikes, canoes, camping gear, etc, etc. And, they had a "Master Key", also known as bolt cutters. This was a large bolt cutter, with handles about three feet long. They let me borrow the cutters, and asked only to hold onto my driver's license. So, I cut the $50 Arbus chain. But there was still a problem. The bolt cutters cut the chain, but not the canvas fabric that protects the chain from scratching the bike. After taking back the bolt cutters, I had to borrow some scissors from the restaurant to cut the fabric.
All the time of stealing my bike, nobody said a word.