Christmas traditions have pagan roots so doing it is a sin:

December 25th: Celebrated as the birthday of various pagan sun gods.
Gift-giving: Encourages materialism, violating the 10th commandment against coveting.
Christmas trees: Idolatrous symbols forbidden by the 2nd commandment (Jeremiah 10:1-5, Deuteronomy 16:21-22).
Santa Claus: A false idol replacing God, breaking the 1st commandment.

The Bible also condemns eating unclean meats like pork and shrimp, and warns against those who disregard the Sabbath:

Isaiah 66:17: Those who eat unclean meats will face God's judgment.
Mark 1: Yeshua's disciples prioritized following him over working on the Sabbath.
Hebrews 3 & 4: Emphasize the importance of Sabbath-keeping by quoting Psalm 95.
Isaiah 56 & Acts 8: Connect Sabbath observance with salvation.
Isaiah 66:23-24: Links disregarding the Sabbath with eternal punishment.