What is the punchline in this joke because I don't get it!!?

You didn't finish the joke; in the end the boss says something like "I was doing fine until the guy next to me said 'Who's that next to Colin??'" Meaning Colin is even more well known then the Pope, which is the punchline, as we initially thought Colin's braggadocious behaviour was absurd and that he couldn't possibly no everyone, but, alas, he does! Hope that cleared things up for you :D