I have gotten so good at this that I can remove her bra without going under the shirt. It's as simple as a two finger snap. Say your making out at a party, no real place to have sex, I will do this and more times then not she will either grab my hand take me into a random bathroom/room... or invite me back too her place!

Visual guide

http://m.wikihow.com/Undo-a-Bra-One-Handed