This was an easy one for me. Of the bikes I've owned, the most useless was the Honda Mini-Trail 50.
Even though it was frugal on gas consumption, it really didn't matter because I sure wasn't going to ride it for distance.
Two up riding was possible (I actually added passenger pegs) but it made for a very friendly twosome and not comfortable for more than once around the block. Acceleration with two on board was virtually non-existent and fourth gear didn't even come into play.
Even riding solo, highway cruising was best left in the imagination rather than practice. Even at WOT it was unlikely you'd need to comb your hair when you arrived at your destination.
The spunky little contender did have some nice features such as the folding handlebars allowing the bike to be stashed in the trunk of your car when someone came along you didn't want to be embarrassed in front of.
At the time it was kind of a chick magnet, but when they got close you realized they were laughing at
you, not with you.
It could turn extremely short, too. If the turning radius was taking too much room, just stop, pick it up, point it in the direction you want to go, sit back down and off you go... in almost a zero radius!
I bought it thinking it would be useful around the farm, especially checking the cow/calf herd. It was a quiet little thing and combined with the small size, not so likely to spook the livestock. There is a down side to the small size... that it put the rider's point of view a little too low if for some reason one ran inadvertently into a cow's hind end. (That story is related elsewhere on this forum). Cattle Roundup
This Honda Mini-Trail also became the bike I owned for the shortest time.