A couple of other nominees...
The Type 95 Ha-Go: Now, this has to be considered a tank in context. While Germany and the Soviet Union were learning (mostly the wrong) lessons from the Spanish Civil War, Japan was already fighting in China. Japan based its armored force on WWI tanks acquired from Great Britain with a big caveat: the were dreadfully afraid of setting their crews on fire. As a result, Japan switched to diesel and lined their tanks with asbestos.
Keep in mind that the Japanese had two grand strategic visions pre-WWII. One, the Northern axis, which favored conflict against the Soviet Union to take advantage of the raw materials and open tracts of land in Siberia. The other, the Southern axis, favored action against resource rich Southeast Asia (binding together a greater Asian empire led by Japan), which would naturally bring it into conflict with the US. Both of these strategies would bog down because events would turn Japan toward a Chinese quagmire--goaded on by uncontrolled elements of the Kwantung Army. However, Khalkun Gol would decide the issue between North and South by terrifying the IJA against the Red Army. The IJA realized that it was completely unequipped to deal with the Red Army across the tank country of Northern China.
The IJA has was already married to light tanks because it was allocated a small amount of armor which was otherwise engaged in shipbuilding and a paucity of fuel to drive heavier vehicles. Of these, the favored was the Type 95 Ha-Go. The Ha-Go was a domestically developed light tank--very light. It had two machine guns and a 37mm main armament. One machine gun was in the bow and the other was mounted at a 4 o'clock position in the turret. The power plant was a 6 cylinder diesel. With the exception of the bizarre 4 o'clock MG, all of these are admirable qualities. It was a nice, simple tank for a country that wasn't going to be fighting big tank on tank battles.
However, the armor was thin. Very thin. 9 to 12mm of armor on the front--barely enough to ward off small arms. The 37mm main armament was of course never meant to take on other tanks. In fact, it would have had a bad time facing any American tank starting from the M2 and virtually any Red Army tank not meant for a completely recon role.
The 37mm gun was insufficient for an anti-tank gun and really not very useful as an anti-infantry gun. It was so bad, in fact, that the commander--the only occupant of the turret--would frequently swing it around to the 8 o'clock position and use the MG instead. It was also totally unbalanced. Because the turret was unpowered, fine adjustments were made by manually swinging the 37 in a 45 degree arc in its mantlet. However, the gun was quite front heavy and swung around like a tongue on a winded golden retriever--especially on an incline. The turret also had an overhang which allowed it to be jammed with the use of a bayonet. I'm not sure how often this was used by close combatting infantry--this weakness was discovered by the British in Malaya (long after when it would have been useful to the Chinese.
However, I refrained from including this in the list of worst tanks because let's face it, the Ha Go seems adequate against the Chinese, where they were sure to face few tanks, few anti-tank weapons and little artillery concentrations capable of targeting a small formation of armor. It was also small and light for transportation on ocean voyages (allowing it to be used in island invasions. It was reliable and easily maintained. All in all, not bad for the context in which the Japanese expected to fight.
Being powered on diesel fuel (which is a kind of by product of the production of aviation fuel), it didn't interfere with the vital nature of Japanese aircraft logistics.
So, while in a rank comparison, the Ha Go is no doubt a really shitty vehicle that, assuming you survive seven years of war within one, will probably give you lung cancer, is in its context not one of ASL's worst tanks. About 2000 were built.
I was also going to include New Zealand's Bob Semple tank, until I realized that it never went into "production." New Zealand, in 1941, very much feared a Japanese invasion as part of a strategy to separate allies US and Australia. It therefore considered commandeering and converting numerous (about 90) Caterpillar D9 tractors with sheets of mild steel (unstrengthened non-armor quality) plates. Bristling with machine guns, 3 prototypes were made before the US, in its mercy, offered up Shermans in 1944. However, threat of invasion by this time the threat of invasion had faded. The worst idea coming out of New Zealand since the inclusion of Taurial in the Hobbit.