Question:
Should I allow people to take advantage of me? Is it okay to retaliate once in awhile?

Answer:
The Bible says, “Avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord. 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: 19-21).

This last phrase is spelled out more in Matthew 5:44: “Love your enemies, bless them that curse you, do good to them that hate you, and pray for them which despitefully use you, and persecute you, that ye may be the children of your Father which is in heaven; for He maketh His sun to rise on the evil and on the good, and sendeth rain on the just and on the unjust.”
There is special blessing for those who behave in this way toward people who are difficult to get along with: “Blessed are they which are persecuted for righteousness’ sake: for theirs is the kingdom of heaven. Blessed are ye when men shall revile you, and persecute you, and shall say all manner of evil against you falsely, for My sake. Rejoice, and be exceeding glad: for great is your reward in heaven: for so persecuted they the prophets which were before you” (Matthew 5:10-12; see also 1 Peter 2:20). In a situation where a fellow employee, say, is taking unfair advantage of me (either to try my patience or knowing that I, being a Christian, will not retaliate), it may be appropriate, occasionally, for me to point out to the offender that I am aware he is taking advantage of me and to thank him for the opportunity he gives me of reaping the eternal reward of patiently responding as Christ would have responded. Or I may respond to each offence by giving the offender a gospel tract or speaking a word for Christ, along with doing what has been asked of me.