Racing Game challenges.
One user sets a challenge which can be completed in any way you specify. The challenge is then picked up by others, who submit videos of them trying to complete it. After a certain amount of time, a winner is declared, and they choose the next challenge.
These challenges can be simple things like "Fastest legal lap of Silverstone in an F1 car", "Quickest shortcut lap of the Monza GP circuit in any car" to silly things like "Fastest lap of Spa driven backwards", "Fastest lap of the Nordschleife in Reverse Gear", "Furthest jump off a specific hill", "Most rolls on a straight" etc.
Let your imagination wander, and think of something you can do on a racing game and see who cab do it best.
Compete on any game you like. From things like F1 2016, Assetto Corsa, rFactor 2 and RACE 07, to others like GT6, Forza Horizon 2 and WRC5, and then weird things like GTA5, TORCS, V-Rally and Super Mario Kart. If you think it'll do the challenge, post it.