My 2008 TM250. Power delivery like a 1970s 125 MXer, footpegs too high, twitchy handling, and rings that last 25~30 hours before they snag on the exhaust port and destroy the barrel (didn't happen to me, but did happen to its current owner). Brakes were unremarkable too.
I stuck with it for a while, but the death blow came on the day I rode it back to back with my 94 YZ250 - despite the TM's better brakes, ergos [apart from the footpegs] and suspension, the old Yamaha was both faster and easier to ride, thanks to its better motor and handling....
The '03 GasGas200 was a bit of a shitbox - paid too much, and then had to give it a full rebuild etc. But it's been sweet since then, so I don't really consider it a lemon.
I guess I've been lucky overall - I've owned an XL175, YZ125L, Alfa Romeo Alfetta, numerous rotaries, and plenty of other supposed lemons and none of them have bitten me.
JD/JE Camiras were actually pretty good cars. Holden fixed the many problems of the JAs, but never properly addressed the stigma.