Curtis Pitts, designer of the Pitts Special aerobatic biplane with great success, went on to design a 2 seat version, but got the run around from the FAA for 4 years when he decided to certify it for production in 1973. (thank you Tony! You're the best!)

(not a 2 seater, BUT, it IS a photo I took of a Pitts Special aerobatic plane)

The FAA struggled with this concept as their idea of a 2 seat certified aircraft was a slow steady plodder like a Cessna 150, not a feisty little dart that could do snap rolls on its take off run and virtually climb straight up.

Pitts wasn’t a fan of the government in general and the FAA specifically. When he was certifying the two place version of the biplane, called the S-2, the FAA rejected his drop test data because testing wasn’t done with a tailwheel. 

So he redid the test and included a note which is part of the official certification record, expressing his opinion using the first letter of each paragraph on the tailwheel application.

https://forums.mudspike.com/t/a-funny-peak-into-the-mind-of-my-hero-curtis-pitts/5470