Further questioning revealed that all of the participants had had anal intercourse, but some did not count it as such if the man did not ejaculate or if the woman insisted he withdraw because of pain.
You should understand that the sizes of both the penis and vary among individuals.
But here's the important thing: when you get there don't make your partners guess -- let them know you'd like them to be careful here or there until you've had a enough experience to know what to watch for.
What constitutes consent for a new experience such as anal intercourse, the first time it happens? And I met this guy.