Contradiction with Proverbs 27:2
This verse advises letting another praise you, rather than doing it yourself, which contradicts the self-exaltation implied in Psalm 34:2.
Proverbs 27:2: Let another man praise thee, and not thine own mouth; a stranger, and not thine own lips.
Contradiction with Matthew 6:1
This verse warns against doing acts of righteousness to be seen by others, contrasting with boasting in the Lord as in Psalm 34:2.
Matthew 6:1: Take heed that ye do not your alms before men, to be seen of them: otherwise ye have no reward of your Father which is in heaven. [alms: or, righteousness] [of your: or, with your]