Pride
Boast
noun, verbal noun, の adjective
When your self has overconfidence in something, that's called pride. You can't shut up about that thing, and you boast about it to whoever will listen.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
自分の不倫を得意気に自慢するとか、ありえないんだけど。
It's impossible for me to proudly boast about my own affair.