The first guy goes: “You know what? My arm is really small, like, really really small. I reckon it’s legitimately the smallest arm in the world”
The second guy goes: “Come to think of it, my head is tiny, I think I have the smallest head in the world”
Third guy goes: “I’ve never told anyone this, but my cock is absolutely miniscule. The smallest I’ve heard anyone having
They decide to all visit the Guinness world records HQ for fun.
The first guy goes in and 15 minutes later he comes out smiling and holding a certificate
The second guy goes in and 15 minutes later he comes out smiling and holding a certificate
The third guy goes in, 15 minutes later he comes out fuming. He slams the table and says: “WHO THE FUCK IS [insert person you want the joke to be about]!”
Edit: Sorry about the ending, but the punchline doesn’t work unless it’s about a friend or someone you know.