If you're still looking for ideas, try this one.
Clip a clothes peg onto each nipple then holding them carefully push hard on each so your nipples become inverted into your tits as far you can. Hold this position for at least 5 minutes but if you can manage longer keep going.
Report back and I will have more games to hurt your tits.
Take 8 to 10 clothespins per tit. Make sure one is attached to the nipple, then circle the tit with the remaining clothespins. Thread a string through the spring of each of the clothespins. Tie a large knot in one end to that it won't pull through the hole in the spring. Now take the free end of each string and tie it to a full bottle of water. Make sure that there is no more than a foot or 2 of slack. Take the bottles of water and place them on a table or shelf. Close your eyes and slowly step back until the bottle fall off the shelf and rip off the clothespins.