As someone who is out in the field a LOT, I've never understood the desire to wear shorts in the rough...sandals either. So, like many above, I recommend pants...and boots. I've been in the amazons and other jungles and for longer periods and will return. However, I'm not a very heat-tolerant type of person. Yes, the heat and humidity is opressive. But I'm not making the trip all that way just to hang around camp. My favorite example of why people should wear pants is from a trip where two companions were warned repeatedly and decided to ignore the advice and wear shorts. Not only were they carved up far greater than me by briars, branches, nettles, but when we got near water, and the no-seeums commenced to swarming and biting (usually waist-level and below), they looked like they either had hyper-measels, or had walked in front of a fan someone had flicked red paint into. I received two bites...on my bare arms while kneeling over the water's edge. My companions had hundreds of bites on each leg. Old Bald Guy is correct...and those same scratches, nicks, etc can become larger, infected, or be all the reason you're noticed by something you don't wish to see or meet. And in jungle areas, no-seeums, sandflies, and mosquitoes prove larger hazards than no wind on my legs. These hazards go WAY beyond a little inconvenient bite. All of them can be vectors for far more serious illnesses and a little cloth barrier can go a long way towards prevention. Oh...and be careful of the candiru.
Anyway Omega - not to [censored] on anyone's parade, but I agree with the others that clothes should be appropriate, and that heat is not the entire story here. While I agree with your statement, "It is better to have 22 calibre pistol in the pocket instead of 45 at home", it looks like you left everything in favor of slightly cooler attire. I don't think the EDC gear that most folks carry will weigh them down while trying to swin ashore. I don't understand how you can't carry gear though. Many people use regular shorts rather than speedos or the swim-trunk style of choice. Many people wear a belt with those shorts. I try to use belt and pockets only as I can't stand anything around my neck. Don't be fooled by shade or clouds...you can get just as painful a burn in those conditions.
Items hanging around the neck seem to just get in the way or be a general nuisance.
I'm not sure I follow your dress code comment though. You were in the jungle. To me, bathing shorts in the jungle seems a mite ridiculous-looking. YMMV
In town, you don't need full tactical gear and/or camo in order to EDC useful items.
Bottom line--I don't even go into temperate forests dressed like you describe. I don't so much carry a specific kit, as a variety of items either on belt, in pockets, or in a daypack (which I'll always have...even if I only plan on an hour or so). No amount of familiarity is going to help you if you sacrifice nearly all levels of preparedness. I do agree that we all do this in some ways that are appropriate for ourselves. I still enjoy cotton...but there are times when I carry backup garments.
...and to be truthful...I can't remember the last time I wore shorts...other than being airy or doubling as swimwear, I just don't find them as versatile as pants.