The shoe being on the other foot here, men can have the same sweaty ballsack and butt stench as the ladies can.
Good solution is definitely to take a shower together, it's very erotic and gets the area clean.
Doing this will only work so many times before the other person might begin to wonder why you want them showered first. I think being honest is the best way to go. If the person stinks, try to tell them in a nice way to clean up first.
I prefer myself to be clean before I let anyone down in my southern region and prefer the same from my love.