I could tell you a joke about TCP/IP...

 I could tell you a joke about TCP/IP, but I would have to repeat myself until you got it.

This is a joke that requires the listener to understand how the TCP/IP protocol works in order for it to be funny. It is also an insult. The reason why this is funny is because one thing that TCP/IP guarantees is that the data being transmitted will be delivered successfully even if the network makes no such guarantee. The way that they can guarantee this is by making the sender of a message retry sending it until the listener has acknowledged that they got the message successfully.

The reason why this is an insult is that the jokester is insinuating that the listener wouldn't understand the joke, and so would have to repeat himself. This is insulting the listener's intelligence, and thus is funny.