Noun, Suru verb, Transitive verb
singing one's own praises; praising one's own wares
Yojijukugo (four character compound)
あいつのことを好きなやつは誰もいない。なぜならあいつはいつも自分のことを自画自賛ばかりしているからだ。Nobody likes him, because he is always blowing his own horn.
Also written 自画自讃【じがじさん】