This will take one hour to do:
a) Rub ice on one of your nipples until it gets hard.
b) Then spank it with a ruler or the back of a wooden spoon, do it very hard for 5 minutes.
c) Repeat steps a and b on the other nipple.
d) Do a, b and c but this time spank very fast (not necessarily hard) for 5 minutes.
e) Repeat, alternating nipples for one hour