it can mean two things:Originally Posted by NewHope
literally it may mean to punish or discipline someone or it may mean "it's awesome!", "it's great", "it's wonderful!", "cool", "it rocks" etc. The latter is used quite commonly by younger people.
How was your date last night?
Oh man, we went to see this kick ass movie and it was really interesting.
"kick ass" here functions as an adjective.
also, you can say "to kick someone's ass" as well and that would mean exactly what it says.
"I am so mad at him I am gonna kick his ass so hard, he will remember me for a while."