He is always boastful about his achievements, which annoys everyone.

boastful 是由动词 boast（吹嘘、自夸）加上形容词后缀 -ful 构成的形容词，表示"爱吹嘘的、自夸的"。后缀 -ful 通常表示"充满...的"或"有...倾向的"。