One fantastic way to torture your nipps at home is using a electric hand mixer (not sure if thats the right word in english.?). I mean the thing you use in the kitchen to mix ingredients when cooking. Put it against you, so nipple is between the mixer "blades?". On one side, they will just spin fast and hit your nipples every time the blade passes it, just like pushing your nipples on a table fan. But when you put it to the nipple the other way around, it will suck your nipple between the blades faster than you realise, and force the poor nipple trough the two rigid metal mixer blades sgueezing it flat and spitting your sore, crushed nipple out the other side. My Mistress used to do it to me every time she tortured my nipples, and it felt absolutely amazing.