Live and let live. By exacting revenge we usually only hurt ourselves more in the process. Unless the transgression was something completely off the scales which deserves retribution (like the person hurting your child) I say leave it be and focus your mind on something positive instead.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~