I learned on a smooth/slick concrete garage floor, then went to a school parking lot, and within two tries I was able to get a full rotation backwards while skidding. put your nuts on the stem dude....

I was also stoked with myself when on the first day I did a skid with one foot while throwing the other leg over the frame and smoothly dismounting when the bike stopped. Do I fully know how I did it? hell no, but I was stoked, more than enough for me.