I'm a fan of humiliation. My g/f and I have been experimenting and progressing for about 3 years now. In public she's a little on the shy side (not the case in private at all). One thing I enjoy is taking her to a sex toy shop and having her buy her own dildoes, clamps and vibes. Being a gentleman, I provide the money of course...but I like to take her to the really sleezy peep show joints and make her buy her toys with the others watching her. It embarrasses the hell out of her and turns me on like crazy. I also recently made her wear a large pair of benwa balls to work for the day so she'd have a reminder of what was coming that night. I like the butt plug idea, but haven't tried that for a work shift yet.