NOT A TEACHER
Hello, Eghbali:
I feel that "kick-ass" is neither polite nor rude when it means "cool."
In my opinion, I think that it is just the kind of "tough" talk that many males like (and probably some females, too).
I think that it's fine if you want to tell your family or friends: "I'm taking a really kick-ass grammar class. There are only 50 seats, but dozens of students were standing in the aisles today as Professor Smith explained the position of adverbs. Man! He is a kick-ass dude!"
I would, however, suggest that you NOT use it when it means to "punish":
Raul: Do it now!
Joe: No!
Raul: You (had) better do it now, or I'll kick your -ss!
Joe: You and who else? ( = You are not big enough to kick my -ss!. You will need at least one other person to help you.)
As you can see, Raul has placed himself in a very embarrassing position.