1. To exert a significant amount of energy in some task, activity, or goal; to work very hard. I've been busting my butt all night long to get this presentation ready for tomorrow's meeting. She's going to have to bust her butt if she wants a place on the varsity team.

2. To harass, nag, or upbraid someone to do, accomplish, or complete something. The boss is busting everyone's butt to get the project ready by next week. Quit busting my butt! I'll get it done eventually!

3. To defeat one decisively. We weren't prepared for the game, and the other team busted our butts.

4. To tease one; to give one a hard time. Aw, come on, dude, I was just busting your butt. No need to get upset about it.