Originally Posted by CityGent
Yes. Provided it's a v-neck or some other cut which won't show even when the top button or two of the polo shirt is unbuttoned, I think that although not ideal, it's perfectly acceptable, particularly when it's 95 degrees and the alternative is having your polo shirt dotted with large, runny drops of sweat.
Wearing an undershirt while its 95 degrees out won't help with the sweat problems at all.
It's always better to buy some better polo shirts that's breathable and won't change color when its wet...