I noticed from some ex when they notice I just wear a short without underwear to nearby places, they always like to tease my lil brother to make it semi erect or erect to show its shape protruding.. Does going underwear-less attract them ?
But I notice some like cute cartoon ones and some like those that material/ design that make your manhood stand out more.. All boil down to personal preferences I guess as I have read before from some local female forums before...