How to Undo a Bra with One Hand

Step 1 - Get some privacy. Get romantic. You want to touch her and she wants to be touched. Start kissing

Step 2 - Remove her dress or shirt to expose the bra. Knowing that the majority of bras clasp in the back and are held together by tension will help you visualize the unclasping. Always best to imagine it before you do it. 

Step 3 - Using one hand. Just two fingers, actually. Gently, but firmly, pinch the clasp making sure to get the straps on either side too. This will relieve some of the tension on the clasp itself.

Step 4 - Snap your fingers (as best you can). If you gathered enough of the fabric and relieved enough of the tension on the clasps (or the hooks) then they should just fly apart and possibly impress your lady friend as well.