Stingray, 1969 or '70. I really thought I wanted one, but it wasn't satisfactory to ride. The novelty wore out quickly. I much preferred my next bike a year later, a conventional 3-speed city bike.
Since then I can make just about any decent bike work. It's just a matter of fit -- getting the right saddle, handlebar, stem, reach, etc.
Well, almost any bike. I still can't get along with a recumbent a friend loaned me a year ago. I think I did one lap around the parking lot, hated it, never took it out again.