The shortest haul flight today is 1.7 miles between Westray and Papa Westray, Scotland, scheduled to take a maximum time of 2 minutes. You even get a bloody certificate to prove you’ve done it.
The current king of the long haul flight is Auckland, NZ to Doha, Qatar, which is 9,031 miles over 17 hours 40 minutes. Bear in mind, however, this title often changes when airlines realise such long routes are massively expensive and there’s not a correlating demand.
Saying that, you could watch the LOTR trilogy twice onboard, and then head to Hobbiton to win the weekly quiz at the Green Dragon Inn. There’s the demand.