ewe! It's typically not a good thing when a guy has wet underwear!
Depends upon what you mean as "wet underwear" for a guy. While women get wet when they get turned on the same is sort of true for a guy in the sense that when they are turned on long enough with a strong erection they will get precum that can wet their underwear but at most we are talking about a quarter sized wet spot. Unless of course we are talking about if a guy goes all the way and **** in his underwear but I don't think that is what you are asking.