Okay, I did some experimenting the other morning. I really don't enjoy (experiencing) pain that much, but I do like to test things out before giving them to anyone, so:
In the Dares forum someone posted a dare for someone to insert a q-tip while hard and masturbate. I'm posting here instead because this thread is much older and more useful for information
So I tried it and couldn't actually come with it in (pain was too distracting for me.) Took it out and carried on, and then felt a massive rush of pain - you could literally feel how far up the shaft the semen got before hitting the sore spots.
If you want to punish your male slaves with completely ruined orgasms, this is the way to go.
(I am so not doing this again. Someone else can continue testing
)