['I like to swim laps, and I discovered that you can see directly up my shorts if swimming behind me.', 'Wow. Must be a sight for those behind you all this time.', 'Yeah, my girlfriend told me about it. I had been swimming in these shorts for weeks before I found out. I feel pretty awkward about going back now.']
It's ok. I'm sure everyone has their embarassing moments.
I was swimming laps one time, and didn't realize that you could see directly up my shorts from behind. I only found out weeks later after my girlfriend told me.