I finally found a gun that was just too small for me to get a handle on: the Ruger LCP. I've mananged with a number of j-frames with boot grips but never found a gun that was just so small I couldn't work it comfortably at all. Yesterday I worked a buddy's Kel Tec P-9 happily. Heck, I even managed a Jennings J-22, Beretta Bobcat, and a Taurus PT-22 but the LCP was just too small for me. It may have had something to do with the fact that I was trying to manage the LASER button on the grip while firing.
We're all looking for the "just right" gun. What have you found that's just too big or too small for you to handle? I'm talking grips, not caliber.