When I was a teenager growing up in North London there was a public toilet that I used to go in because there was a glory hole through to the ladies toilet and a few times I had peeped through it and seen women using the toilet and a couple of times I had been sucked off there.
One day I went in to the cubicle as usual and could see from the waist down a girl in there masturbating, I started stroking as I watched her and eventualy pushed my cock through the hole, after a few seconds the girl started wanking it and then she began to suck me. She was a great cock sucker and it was not long before I shot my load into her mouth, after I zipped up and left the toilet but wanted to see what the girl looked like so hid just nearby and watched. After about 10 minutes imagine my surprise when out of the toilet came my sister.
The day after when she left the house saying she was going for her usual walk I followed her and sure enough she went into the toilet again and again I went into the cubicle and stuck my cock through getting beautifully sucked off, this time though I did not hide to watch her come out but waited at the toilet door.
When she came out and saw me there she looked a bit uncomfortable and asked what I was doing hanging around so I said "Oh nothing much, but I just got my cock sucked off in the toilet". She looked at me and stammered you mean you, Oh my god, she turned aside and vomitted into a trash can.
I said " was it really so bad" and put my arm around her as she was sobbing her heart out, mumbling I am so sorry. we walked home like that and when we got indoors I said "its OK no one will know" and kissed her full on the lips. Well she wasn't that mortified because she had my cock out and was giuding it to her c**t in no time, we fucked twice that day before mum came home and me and big sis have been fucking our brains out ever since (16 years now). We now 'share a flat' but in reality we only use 1 bedroom!