Thomas Aquinas

“ In another way a man uplifts himself in words, by speaking of himself above that which he is in reality. And since we should judge of things as they are in themselves, rather than as others deem them to be, it follows that boasting denotes more properly the uplifting of self above what one is in oneself, than the uplifting of self above what others think of one: although in either case it may be called boasting. Hence boasting properly so called is opposed to truth by way of excess. ”

“ Unless perchance he were to prefer this to the love of God, so as to contemn God's commandments for the sake of boasting: for then it would be against the charity of God, in Whom alone ought our mind to rest as in its last end.
To boast for the sake of glory or gain seen to involve an officious lie: provided it be do without injury to others, for then it would once become a mischievous lie. ”

“ For sometimes a man speaks of himself, not above what he is in himself, but above that which he is esteemed by men to be: and this the Apostle declines to do when he says (2 Cor. 12:6) : "I forbear lest any man should think of me above that which he seeth in me, or anything he heareth of me." ”