“See that none render evil for evil unto any man; but ever follow that which is good, both among yourselves, and to all men.”  
1 Thessalonians 5:15

The main verse is repeated in the book of 1 Peter
“Not rendering evil for evil, or railing for railing: but contrariwise blessing; knowing that ye are thereunto called, that ye should inherit a blessing.”  1 Peter 3:9
And repeated in the book of Romans:
“Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord.” Romans 12:19
So God is serious about how you perceive evil that has been done to you and how you respond; don’t curse, don’t repay, he says avenge not yourself!
“Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head.  Be not overcome of evil, but overcome evil with good.” Romans 12:20-21
He says overcome evil with good, meaning doing good is more overpowering than evil, so instead of remaining in the low level of evil deeds, he says don’t bother avenging yourself; if you do evil, nothing will change, but he says you can and should overcome the evil done to you by doing good.
You can and should overlook the evil done you by following the good that person has done or the good in the person. Don’t plot your vengeance, bless instead.