Undies Race

i'd say some very form fitting boxerbriefs- like ones that are pouch where your junk is out front- and that show off your great V abs. Something like this: Sweat Under Gear Underwear Sweat Trunk 5001 from Topdrawers Mens Underwear

Then you can show you have taste and keep your monster junk basically covered- and those who really want to check you out can do so as well.
 
I had a pair of red, white and blue running shorts with the white in the middle crotch area. Whenever I ran and got sweaty, the white would become transparent. Freeballing with them really got everyone's attention. If you are going for the shock factor, find something lightweight and white. If not, go for something dark.