The little boy was often teased by his classmates for his noticeable bucktooth.

bucktooth 是由 buck（原指"雄鹿"，这里引申为"突出"）和 tooth（牙齿）组成的复合词，字面意思是"突出的牙齿"，特指"门牙突出"这种牙齿特征。