As soon as the boss entered, he started boot-licking and flattering excessively.

boot-licking 是由 boot（靴子）和 licking（舔）组成的复合词，字面意思是"舔靴子"。这个短语源自古代臣民通过舔统治者的靴子来表示极度服从的行为，现在用来比喻"卑躬屈膝、阿谀奉承"的行为。