I made 2 of them with thumbtacks. You take a bra. You buy thumbtacks at a stationery store. Depending on how much pain you want, you insert them on the outside (less intense) or stick them inside the bra (more painful). Really very effective and easy to do. I alternate between the 2 models. To add pain, you can take a bra smaller than your usual size. You can then knead the breasts, tap them or just carry it.
Außen unscheinbar, aber innen