Reassembled from partial quotes in archived forum messages by: Kosh
The author writes:
To celebrate comic number 90, I'm holding a Caption Competition. If you want to participate, go to the forum thread and enter your content for the empty speech bubbles.
I'm 100% sure that everybody who hasn't lived under a rock in a cave for the last 25 years recognises the character who has a cameo appearance in the penultimate panel (and should provide the lead to the punchline...).