When shopping, open the fitting room curtain right while he's trying something on and completely naked except for panties…and keep it open while the sales woman brings in a different size or comes to comment.
Do this whenever possible, but when he least expects it....just for fun. It must be a surprise. You will need to find do this when you are in a shop with a one or two nice shop assistant women who look like they are open minded. Use your feminine charm to let them understand that they should play along, and let them go as far as they want… maybe even getting them to comment or suggest things. You can do this in the company of any other females (but no men). The impact is of course much more intense if the other females are attractive to him, as he will feel more humiliated. It will also help if the other females are noticeably laughing or amused at the situation, and are even able to say something to him that regarding how much of a sissy he is.
Do this when he's wearing panties and a chastity device and he is in a fitting room. Pre-arrange with a female shop attendant to suggest him feminine shoes and clothes. If you know of a shop that sells both men’s and woman's clothes, lure him in to look at clothes and try things on. The best thing to do is to remove his pants from the fitting room to "check the size" and then keep them in your hand while you swing open the curtain or door and have the sales women bring in a garment his size. Have the shop attendant openly suggest to him more feminine items, and make him try them on, while she keeps bringing him more feminine items to try on. You may want to ask the sales person if she thinks the things he's trying on fit well, to have her comment. You should ask her if there's anything she suggests he look at, and (without him seeing) get her to encourage him to try on something obviously feminine, like a blouse or some accessory.
Just the suggestion that he try some feminine things from a female shop attendant is very strong psychological public humiliation. Since it will come as a surprise to him in front of you, he will see it's also someone else’s affirmation that he appears to be a sissy. Your job is to reinforce this by agreeing with the shop attendant and encouraging her to suggest more things while insisting to him that he should accept he suggestions and make him come out of the fitting room each time to show everyone how it looks. It will also humiliate him that you are agreeing with the sales woman and forcefully insisting that he to listens to her.
He will be literally caught with his pants down and have no place to hide. This will be a very embarrassing moment for him, as will have standing there in only panties or with tan lines. This is sweet and cruel public humiliation that you can spring on him when he doesn't expect it in front of a young nice sales woman. The point is to thoroughly embarrass him when he least expects it right in front of another beautiful woman. It also certifies to him that you are not afraid to expose and humiliate him. He will develop a whole new fear for your authority and appreciation of your demands.... besides, it'll be just really fun laughing at him together with someone else!
You should simply not acknowledge this is an embarrassing situation for him, but instead act as if it’s perfectly normal. You should act completely normal and at ease as you expose him. As if you hardly realize that you are embarrassing him and humiliating him so much. Your attention should be focused on the benefit of the amusement of the other women watching. Tell him that you think it’s about time people know he's a sissy. Tell him that he seems surprised that you are doing this to him, and remind him that you are perfectly comfortable with exposing him on any occasion, so he better behave and obey you. However, it could also be used as a spontaneous way to punish him for not obeying you in another occasion…as long as you let him know what you are punishing him for and make him understand that he earned such a humiliation.
You should be dressed normally with no special preparation; however you should do this only when you know he's wearing feminine lingerie (which he should be all the time!).
Don't do this if there are men around, it would be a total turn off. Make sure you expose him to a point where he really feels embarrassed or full of fear of humiliation. Try a small shop where the women working there have some flexibility and would otherwise be bored. If he buys something, make sure he gets them to mark the alterations, then send him back alone to pick it up and try it on. Make sure there are only females around. Don't get nervous while you are exposing him…instead you really need to convey your confidence.
It's a beautiful scenario that must be tried.