Man, I don't think I can even choose.
I've made a metal detector go off at a government building I didn't know I'd have to enter, while my wife/keyholder was out of town. I had to explain to the guards why I set it off. The two male guards were very professional and used a wand to check everywhere EXCEPT my crotch, and then discreetly waved me through without even changing expression, but a young female guard who was monitoring an x-ray machine for backpacks and purses stared and smirked at me throughout the entire ordeal. She didn't even pretend to hide her amusement.
I've flown on planes caged, probably no less than 12-15 times. My wife was cautious about it at first, only leaving me caged when the two of us were traveling together. After several times where nothing happened, she started leaving me locked when I was traveling by myself. Then last year, on a work trip with several coworkers, I was stopped by TSA, and taken to a back room where I had to drop trou and show my caged dick to three agents. As humiliating as it was, it was almost far worse. I was extremely lucky that I had chosen to go to the restroom before going through security and my coworkers had gone through ahead of me. When I caught up to them at the gate, they thought I'd taken a really long time in the bathroom, but didn't know I'd been taken aside for show-and-tell with TSA.
Those are the only two instances that were accidental. My wife periodically enjoys making a game of humiliating me, sometimes enlists the help of others or sets me up to be found out when she's not doing it directly herself. She doesn't intentionally involve family or professional contacts, and she's got to be in a particular mood, but she's very devious and creative.
I've had to wear my cage at a gym while we both worked out, on an evening we had plans immediately afterwards. She knew I'd need to shower there, in the men's locker room, and that there were no stalls separating the showers. As we left, she asked me how many men I thought noticed my little cage.
She's booked full body massages for me, for occasions like my birthday or *******'s day, with a massage therapist she knows I find extremely attractive, and a couple times left me caged, "so I won't get an embarrassing boner when the pretty lady rubs me." Once she had me wear my bulkiest cage, "to see if she notices the interesting shape under the thin little sheet." To this day, I'm honestly not 100% sure whether she did, but her wrist definitely knocked the side of the cage when she was adjusting the sheet to rub one of my legs, and it sure felt like there was an awkward halt in our conversation.
I was once invited to a shared birthday party for three LS ladies, and told to bring a massage table so I could give them full body massages. My wife asked if the birthday lady who invited us had any wardrobe requests, and sent pictures of all the "manties" and jocks and thongs and skimpy things she's ever bought me. Her friend chose a pair of open front pink briefs that left my entire package hanging out in the open, and my "I'm a lucky cucky" shirt. None of the lady's friends had seen a cock cage before, so she invited them all to examine and touch it. Out of the maybe 20 or 30 people in attendance, 2 were hung black men, and my wife fucked one of them in the middle of the room while I was paraded around by the birthday girl.
Four of my wife's vanilla friends (that I know of) know I'm kept in a cage, and two of them know she's a size queen who fucks black men. They've both seen dick pics of one of her bulls, and one of them has seen pics of my caged dick, "for comparison." That one now shoots me knowing grins every time she sees me, and subtly bosses me around, having me get her drinks and such.
On a night we were out dancing, my wife found out the lady she was talking to liked BDSM, so she sent me into the women's restroom with our new friend, to "show her our new cage." Twice after that I was lent to that lady to be spanked, teased and service her orally.
At two separate bars my wife was asked what the key on her necklace was for; once by the bartender at a typical bar, and once by a lingerie vendor at a LS nightclub event. Both times she answered without batting an eye, "it goes to the cage I keep his dick locked up in," nodding in my direction.
During another time my wife was out of town, she mailed a key to another cuckoldress, and asked her to unlock me so I could take a supervised shower midway through her trip. Our cuckoldress friend scheduled my release for an afternoon when her bull was coming over, I was stripped and knelt on the floor of her bedroom with her naked hubby while her bull plowed her in front of us, and then showered and made to edge while she unlocked her hubby and let him have sloppy seconds. They fucked on the bathroom floor in front of the shower and he got to cum right after I was told to stop touching myself.
I've had countless photos of various cages, silly undergarments and size comparison pics with objects like chapsticks taken when I was soft and at my most retracted, sent to my wife's select girlfriends and bulls.
I really can't say which of those was the most embarrassing, and I'm sure I'm forgetting many other contenders.