Maybe you only have the one hand. Maybe you want to show off. Maybe you're just too cool to deal cards with both hands. Whatever the reason, this is a skill that will elevate your status from card player to master card manipulator. Okay, maybe not. Still, it's fun to do.
(See the youtube video clip)
Step 1: Mechanic's Grip
The thumb rests across or near the upper left corner of the deck. The index finger supports the cards by the top edge of the deck, and the remaining three fingers grip the deck on the right edge.
Experiment with the vertical positioning of the deck. Initially, I tried holding the cards closer to the top edge, so that the lower right corner of the deck stuck out of my hand. I later found that I was able to get more leverage on the cards (later steps) when I held it in a normal mechanic's grip (dealing grip).
Step 2: Grip the Card Between Your Fingers.
At the same time, bring the middle finger down on top of the card, pressing down on it next to the ring finger. Lift the thumb off the card, and press down on the card with your middle finger. The top right corner of the card should be pressing against the rest of the deck, causing the card to bend slightly.
Step 3: Flick!
Step 4: Final Notes
I have never seen this sleight anywhere else, so I'm going to claim creatorship of it since I did think it up myself. Please let me know if you know of a previously published version of this.