When I was thirteen I had these yellow pyjama shorts. One night I pulled them up very high so they were very tight and gave me a wedgie. I was then lying in bed on my side. I started to feel my butt cheeks that stuck out from under the shorts. I rolled over to the other side. The moment the front of my shorts hit the blanket I felt a very strong tickling feeling in my penis. I then started rubbing on the blanket for about ten seconds before I exploded with my first orgasm.
Today, after nearly 20 years of repeating this event not much has changed except I now use my hands a bit and wear a g-string to do it.