The craziest, i.e. riskiest, thing that I have done would probably be having sex in "public" while diapered. I put public in quotes because there wasn't anyone around, but we were on a hiking trail in the woods along the water where someone could have walked by and seen us.
Both of us hiking on a trail near a lake, we got horny and decided to fool around in the woods. Since the park was deserted and unlikely to have anyone around, my husband dared me to take off my clothes and walk along the trail in just my diaper. I undressed and put my clothes in his backpack. We walked for a few minutes like this, with me in front of him so that he could see my diapered butt walking in front of him.
He got very turned on and wanted to do more. While on the trail, he unzipped his pants and pulled out his cock and stroked it a few times. I got down on my knees and started sucking on it. It was very risky because had anyone come down the trail, there would be no explanation that would tell a different story. There was me wearing nothing more than a diaper, on my knees sucking on another guys cock. We realized this, and decided that if we were to finish that we better move to a more secluded place.
We left the trail and found a hiding spot down an embankment. No one would be able to see us unless they happened to leave the trail in the exact spot that we did. Once hidden, he got a small bottle of lube out of his backpack and pulled down the back of my diaper. Lubing his cock and my ass, he slid his cock in and fucked me. He didn't last too long because the thrill of getting caught was so high. Once done, he pulled out, pulled my diaper back up, gave me my clothes back to get dressed and we continued our hike again for a few more miles. The whole rest of the hike I could periodically feel the cum leaking out of my ass and into my diaper.