1. rude slang One who tries to motivate and inspire people toward some goal or end. The new boss is a real ass-kicker, but we've never gotten so much done in one quarter before.

2. rude slang Someone or something that outshines or surpasses everyone or everything else. This new system is a total ass-kicker—we've never gotten so much done in one quarter before.

3. rude slang A particularly raucous song, usually in the rock genre. I just heard "Sweet Child O' Mine" on the radio, and it's still a real ass-kicker, if you ask me.