“Do not boast about tomorrow, for you do not know what a day may bring forth. Let another man praise you, and not your own mouth; a stranger, and not your own lips” (Proverbs 27:1, 2, NKJV).
Boasting and “trash talking” about how great we are can be a temptation sometimes, and in the world we often see this valued highly. This is the opposite of the humble attitude that is pleasing to God.