There is absolutely no way I could narrow this one down. Not even close.
If we extend it out until 40 years and three days, I would've liked to have been there for Hank Aaron's 715th home run, watching him getting a standing O in the Deep South in 1974 would probably be the most amazing experience.
Other than that, I would've liked to have been in Japan for Lib Tech's Holy Bowly last year. That would've been a super fun course to ride.