Forests are not usually ranked on a scale from friendly to unfriendly to downright mean, but my travels in the tropical rain forests on all the continents have suggested that such a ranking is not only possible, but maybe even meaningful. The rain forest in Uganda ranks among the friendliest, by which I mean that there are few dangerous or spiny trees or plants, temperatures are mild, the forest floor is fairly open and not too tangled in vines, and the trees are of a range of sizes, fairly well-spaced. OK, so there are the usual poisonous snakes and some pretty impressive ants that flow in floods over the forest floor, not to mention the forest elephants that move like shadows through the woods. Borneo with its forest of staggeringly huge, emergent dipterocarp trees, are pretty similar on the friendly scale.
On the other hand, in Central and South America, the rain forest is a bit less friendly with a number of spiny trees and palms that you wouldn't want to climb in case you got attacked by peccaries, and a few of which rain stinging ants upon your head when you bump them. There are also some pretty mean wasps and ants that warrant attention.
But in Australia, the forests are just plain mean. You cannot walk through an Australian rain forest without monitoring all around and checking every step you make. A moment of inattention as you sight a shimmering, flickering butterfly, and you have brushed against a stinging tree, and your skin is on fire. The fire will burn itself out in a day, but its ashes are an unpleasant prickling sensation that can last for weeks. Sure, Europe and America have the stinging nettle, but this is a TREE, and it is layered and mixed with other forest trees, and thus not easily spotted and avoided.
Next we have a truly diabolical climbing palm (yes, a palm that climbs) known as wait-a-minute (aka lawyer cane, because once it gets ahold of you, you will never get loose). This palm has a weak trunk encircled by spiral after spiral of sharp, projecting spines, and produces very long canes from its leaf fascicles, canes that have extremely sharp, recurved spines every couple of inches. Being thin, these canes form thickets of looping arches just waiting for you to bumble into them. Once you run into such a thicket you cannot simply back out, because the spines point backwards and backing out simply digs them deeper into your skin. No, you must grasp each cane, one by one, and carefully pull it out of your now bleeding skin, then try to back away without getting hooked again.
To be fair, this meanness did not evolve to punish humans, although if you ascribe to Intelligent Design, this would be a reasonable assumption. The palm has become a vine, a structural parasite that climbs up into the forest canopy, to reach the light without investing in a heavy and expensive trunk. The looping canes with their recurved hooks droop over to anchor the growing palm in surrounding vegetation, and the palm gradually "climbs" to the canopy.
So by my ranking, Australian rain forests are just plain mean. I didn't even mention the snakes yet, but god help you if jerk back from a stinging tree, and thereby get tangled in a thicket of lawyer cane, while simultaneously stepping on one of the 60 species of lethally venomous snakes. You wouldn't even be able to bend down to kiss your ass goodbye.
Well done. My only experience with 'mean' trees were the Black Palms in Panama. If you lose your footing on a muddy mountain trail, your instinct is to thrown your arms out to grab something, anything to keep from sliding a dozen yards back down the trail. As you described for others, the Black Palm is studded with rings of two inch long thorns, grabbing a handful of trunk impales your hands. I brushed up against one and the thorn stuck me just below the knee. Months later, back in Washington the remnant of the thorn pierced through the skin above my knee when I could finally pull it out.
It's interesting that my interest was much more focused on the details of the naughty forests than on the pleasures of the nice ones. I really enjoyed your concept of ranking forests. Maybe we could use a metric Tschinkel Scale, with 10 Tschinkel's be most heavenly, 0 most hellish.