Passing through IND Center airspace a few years ago we got a hand off to the next sector. So my FO tries a couple of times to check in with no answer. He switches back to the previous frequency to verify the correct frequency is dialed in. Sure enough it is. We go back and try he tries again three more times and no response. When he is about to try again I tell him to let me.
ME: "Indy Center, Jetlink 1234, level at FLXXX, sixth call."
Immediately and without missing a beat...
CNTR: "Roger, Jetlink 1234, first response."
Another time we were coming up from south TX in the EMB120 days in IAH. They assigned us a runway 27 with a resulting looooong downwind vector. Eventually the controller gave us the base leg turn and descent. We responded with the instructions and started the turn/descent.
A minute later the controller comes back:
"Jetlink, 1234, turn left 360 descend to 4,000."
ME (not being a dick): "Yes, approach we copied that and responded the last time."
Controller: "OK, wasn't sure I heard the readback."
ME: "Well, we are so far away from the airport it probably hasn't arrived yet."
Controller (laughing): "So how does LCH (Lake Charles, LA) look?"
ME: "Clear and a million. Thought we were landing there for a minute."
Finally, overheard on another flight (I forget the airline):
Controller: "Airline 5678, contact center 123.45."
Pilot: "Roger, 132.45, Airline 5678."
Controller: "Check that frequency...123.45."
Pilot: "Roger, we copied 132.45."
Controller: "No, sir, you have your numbers mixed...1-2-3 POINT 4-5."
Pilot: "Ooops, sorry about that. I used to be an airline CEO in my previous life."