"I once brought a honeycomb and a jackass into a brothel..."
Tyrion first started telling the joke way back in Season 1's A Golden Crown before being interrupted by Lysa Arryn, before attempting it again in the Season 6 episode No One, only for the slavers to attack and once again foil the delivery of the punchline.
The internet has provided a couple of potential punchlines, both of which fit with the Imp's sense of humour, but we'll never know for sure until Tyrion himself gets to say it - which he surely must, right?
NCTJ-qualified journalist. Most definitely not a racing driver. Drink too much tea; eat too much peanut butter; watch too much TV. Sadly only the latter paying off so far.
A mix of wise-old man in a young man's body with a child-like wonder about him and a great otherworldly sensibility.