Earlier quoted context omitted.
This one's actually not that hard to explain. Shirts can be worn under your armor, and these are the only two kinds of shirts. Normally, a shirt adds nothing to your armor class, but it can be enchanted (up to +7 safely), so it's nice to have one if you can find one. The problem with the Hawaiian shirt is that shop keepers will assume you're a tourist, and charge you extra.
> The problem with the Hawaiian shirt is that shop keepers will assume you're a tourist, and charge you extra. Absolutely cannot tell if you're fucking with me, or if this is an actual game mechanic - and if so, why this shirt would be desirable.
Welcome to the world of nethack! The amount of special case situations that have been programmed into this game over the last few decades are truly amazing. (Mostly because it somehow still works.)
I still remember the first time I ran into a kitchen sink.