Waistcoat only?

[Livonian]

I can't speak for the tropics, but here in Michigan, we get a horrid combination of heat and humidity. Smart-Smart is a no-go in summer, unless you like dehydration and heat stroke. Shirtsleeves, with a vest at most, is all that can be reasonably worn without risking one's health. Shirtsleeves-and-tie and/or vest-only are not only for teens being forced to dress nicely, but for adults who dislike heat-related illness but still wish to be presentable.

[Sir Didymous]

I actually just commissioned my seamstress for a grey (with a hint of light lavender) waistcoat for casual spring/summer wear. I will not be getting a matching jacket.

[OC Richard]

At our recent Sacramento (Woodland) Games waistcoats and brimmed hats were perfect for the weather (chilly when the sun went behinds clouds, brutal sun when not)