i think when designing something to be printed on underware things should be avoided, such as the shapes that would resemble certian body parts, the baloons kinda look like a pair of nuts....they don't come accross quite clearly enough as baloons, they kinda merge together, i think that is the main thing.
upside down nuts? hah i get what you're saying and i think it takes a slight bit of a stretch to see the balloons.. but what else could it be.. that is taking the little dude out into the air? surely not a pair of nuts.