I had never heard of a circle-jerk until my freshman year in college.
From time to time, my room mate and several of his friends would go into the dorm room across the hall, where two other members of the jerk circle lived. I never was invited and only heard about them from my room mate when they were over.
These were the same guys who would get someone to buy them a few six packs on weekend nights and go drink beers until a few of them had vomited and had to be carried back to the dorm in the early morning hours.
I never really understood what the purpose of a circle jerk was, or why supposedly heterosexual men would participate in them. Was it to see who could come first or shoot furthest? And why make a contest out of something that is usually private?
I'm actually glad I was never invited. I knew I was gay, but was very, very closeted. There would have been no way for me to stop my eyes from bulging out at the other guys' cocks or wanting to reach out and help two at a time with my hands.