"But I say to you that whoever is angry with his brother without a cause shall be in danger of the judgment. And whoever says to his brother, 'Raca!' shall be in danger of the council. But whoever says, 'You fool!' shall be in danger of hell fire. Therefore if you bring your gift to the altar, and there remember that your brother has something against you, leave your gift there before the altar, and go your way. First be reconciled to your brother, and then come and offer your gift."
-Matthew 5:22-24

This passage is basically warning you not to get angry with anyone and call them names. Work it out with that person. I think the gift that is mentioned here is your offering because an offering is like a gift to God. When you're angry with someone, God cannot accept your gift. You must first forgive that one person then give your gift. I may be wrong, though.