Sarah... this is a slang expression and should not be used in formal and written business situations. It is usually used orally and should not be used with people you do not know well. kick (somebody's/some) butt... (American & Australian very informal... slang) kick (somebody's) butt... also... kick some butt 1. to fight someone and hurt them ... kick (somebody's) butt/ass - Jack told me that he was going to kick my butt/kick my ass. - If you don't turn the music down (reduce the volume), I'll kick your butt/I'll kick your ass. - My friends and I are going to find the guys who hurt my sister and we're going to kick some butts. 2. to defeat someone completely ... kick (somebody's) butt/ass - Our football team defeated the other team by seven goals. Our team really kicked their butts. - The new computer operating system (OS) is excellent. It kicks all other OSs' butts.

You can! Both 'I kicked butt' and 'I kicked ass' are correct for past-tense usage.