I admit it. I totally tried on my Dads underwear and jock from the time I was about 12. He has a big dick and used to wear "Munsingwear Kangaroo Pouch briefs". I remember them vividly. They had a huge pouch on the front that there seemed to be no way I would ever fill that up. Same with his jock strap. Had a huge pouch and I would try them on and they would never fit my waist so my boner would be holding them up with my skinny legs sticking thru the leg openings.
When I was a little kid my Mom would buy my brothers and I "little boy briefs" like Jockey and Hanes. Then one of my older brothers starting buying the bikini "Elance" briefs in the early 80's. (Anyone remember Jim Plamer in his jockey elance briefs that came three in a tube?) and so I started to try his on and buy them for myself when I was about 15 or 16. Until one morning my Dad came in to wake me up and saw me in them with morning wood and I was sticking out the top. Those bikini briefs didn't allow much room for growth so it was baically just holding my balls in. He said that they were ridiculous and I needed something with a bigger pouch and room for my erection. "At your age you probably are getting alot of erections and it's not safe or healthy to not have my penis supported" So that night I came home and found some "Munsingwear Kangaroo Pouch briefs" waiting for me on my bed.
Not much was ever said again but looking back it was a proud day for me. I had actually filled out the same pouch as my Dad. (at least in my size)
I still have an underwear and jockstrap fetish. Thanks for the thread, and thanks for the support Dad.