boaster:
(plural: ‘boasters‘; pronunciation: the letters ‘oa’ rhyme with the letters ‘ow’ in “bow” or “low”)
(old usage) a person who talks too much and too proudly about him-/herself (boasting);
a bragger; a blowhard; a braggart,
a boaster boasting about his huge body
Sandra is a very clever girl and gets the top rank in any exam, but she’s never a boaster, unlike others who boasts once they get some good grades in a couple subjects.
Nelson is a great fellow; you’d love to be friends with him, but his only weakness is that he suddenly becomes a terrible boaster when it comes to his website which has some hundred viewers a day!
Most boasters are like addicts; though they know that half the things they say are lies and that people just listen to them out of courtesy and not because they really believe them, they cannot stop boasting.

