My sister-in-law is a pretty wild 17 year old. She was grounded last weekend for coming home very late having been out with a boyfriend, and her parents asked if I could stay at the house with her while they went to a party, to keep her out of trouble. I agreed as I knew my wife would be going to the party with them and her sister is young and hot.
She has blonde hair and c-cup breasts. I know this from pilfering through her panty drawer. At any rate I went over to her house and after the parents left Kelsey said she was going to go downstairs and play on the computer. I stayed upstairs and after about 20 minutes of looking at all her pictures around the house started to feel horny. I have jacked off with pictures of her thousands of times, have used her panties and bras when they were out of town, and even watched her laying out and beat off in the bathroom. Well I decided to go into her room and look around, I knew where her panties were and opened the top drawer of her dresser. I pulled out a pair of satin bikini panties, light green.
I lay on her bed and pulled my shorts down. I began to stroke my cock with the butt area of the panties. As I was moving the soft satin up and down on my now hard cock all I could think of was Kelsey. I was into this session for about five minutes when I heard Kelsey say 'What in the hell are you doing'. I jumped up and tried to pull my shorts up. All I could say was that I was lying down. I mean what do you say to a girl who just walked in on you jacking off with her panties.
She asked me 'What were you doing with my panties' She called me a pervert and left. I pulled myself together and went downstairs to talk to her. I told her that sometimes men get horny thinking about girls and that she had made me horny. She said she knew guys jacked off, but was just surprised to see me doing it with her panties. I told her I was sorry and asked that she not tell anyone. She said maybe, and asked me to buy her some clothes when she gets done being grounded. I told her that I would do anything so as not to be caught by her parents. I went home that night and beat off looking at one of her pictures and thinking about her walking in on me. I shot a huge load all over myself.