Now to understand this story, you must know that I'm in a wheel chair.
My wife and I are hanging out with a couple of our friends, when I start picking on her. It's something we do all the time. I'll start calling her names, and she'll call me names. It's all just for a laugh, there's no malice behind it. Well, I'm sitting in the middle of the living room with my back to the couch on which is sitting one of my wife's friends (no names to protect my own ass from retrobutions). She sneaks up behind me and starts to tickle me on the back of the arm, right by my armpits. This has to be my most ticklish spot and she has devilishly long nails. Now, since I'm in a wheel chair, and she's behind me, I can't grab her arms nor protect myself in any other way, and since I'm laughing so hard, I can't get away very fast. She chased me around a little while until she stopped because she was laughing too hard at me.
I made sure not to turn my back to her for the rest of the evening.