I would've done a fair few single-car coasters by myself: wild mice, spinners etc.
The coaster that sticks out though is G5. It was just after park opening, and the park was really, really quiet. There were still some people around though, standing on the bridge next to the drop and around the station area, but nobody wanted to get on it without watching it first.
Anyway, I got the first car of the day, by myself, with an audience of about 20-25 Taiwanese, a bunch of which grabbed me at the exit and made me ride again with them.
Very bizzare, but pretty cool at the same time.