Use a cupping set, snake bite kit, or breast pump to suction then for 10-20 minutes first. The bruising and added blood flow makes them crazy sensitive!

Also lining a bra with tacks but putting them through the foam inserts and taking them on, then inserting the foam inserts back into the bra. The tighter the bra the better so a sports bra is ideal. The fewer tacks the more painful each will be, and the more tacks the wider the area tormented will be. Every movement gives a scratch or a pinch there gets even worse with sweat building and time against the skin. You can put it on at a park then lock your other top in your car so you can't take it off. Then walk out as far as you think you can take it away from your car. Now you're at your limit but have to suffer through it getting far worse and the long, slow, agonizing journey back. You can take a break, but it'll hurt worse when it's back on, AND you might get caught. Add in an egg/panty vibrator on a tease setting and you can be in for a wild time. Or line a pair of too-tight panties the same way! Or do both!

Tack bras are also super fun for groaping & slapping & beating tits when wearing them because of the extra pinching scratching pain. You can even wear it while getting fucked!