I was actually creating a RFID vibrating tag for a different project.
For this prototype I used a commercial give-away pen.
To make the pen vibrate I used a motor from an old telephone and used a pensil tip to make an inside carrying construction to keep the motor in place. when I had the vibrating end ready and gave it a testrun someone asked if i was making a vibrator. I said well, no, but I can do that too. I used a second end of a pen to make the battery housing and added a Reed-contact as a switch. if the Pen was removed from the cover the motor would spin. or actually the two motors since I managed to build two engines in one tip.
I made an improved version with a recharable battery inside and a second cover that works as a USB charger. The pen has a diode inside to prevent discharge. i named it the Vibezz, the photo shows a normal pen and the Vibezz and from outside there is no difference. See the Youtube link to see both versions spin. very funny :)